Luther Burbank: His Methods and Discoveries (1914)


All the raspberries commonly known to the cultivator, and many new ones that I imported from Asia and the Southern hemisphere, were growing on my grounds from 1890 to 1900, and were intercrossed very extensively. Numbers of highly interesting hybrids were thus produced, and at least one of these was of so distinctive a character as to merit the title of a new species.

The Dictator Raspberry
This was another of the crossbred raspberries originated at the same time with the Eureka. This also is a mammoth bright red berry. It combines the flavors of the Gregg and the Shaffer's Colossal, from which it originated. The combination is one of the happiest, as the acidity of one is modified by the sweetness and the aroma of the other.

This was the fruit that was introduced as the Primus berry.

This highly interesting fruit, one of the first plants of any kind that could properly be termed a new species to be developed under the direct guidance of the hand of the experimenter, was the progeny of a hardy little berry indigenous to Siberia and Russia, called the Siberian raspberry (Rubus crataegifolius), and the California dewberry.

The little hardy Northern raspberry bore fruit about the size of a pea, of a dark mulberry color, with rather large seeds, and a flavor not such as particularly to commend it. It is, however, remarkable for its large palmate leaves, and the sturdy growth of its stems.

The California dewberry, Rubus vitifolius [=R. ursinus], is a trailing vine which is extremely variable in foliage, habit of growth, size, and quality of fruit. It is found wild everywhere in the foothills and lower elevations throughout the Pacific slope of the United States, but seems to be at its best in Northern California and Oregon. The berries of this wild species are often produced abundantly. They are black, usually of good size, and of superior quality. They are often gathered in large quantities for market and home use.

The Primus Berry
This highly interesting plant is one of the first that could properly be termed a new species developed under the direct guidance of the hand of the experimenter. It is the progeny of the California dewberry and a hardy little berry indigenous to Siberia and Russia, called the Siberian raspberry. The remarkable Primus berry appeared as a first generation hybrid, and it breeds true, having the characteristics of a new and permanent species.

The fact that the dewberry bears so-called dioecious flowers—that is, flowers of opposite sexes on separate plants—has discouraged a very general cultivation of the plant. It is necessary to grow both male and female plants to ensure fertilization, and fruit growers do not relish the idea of having half their vines unfruitful.

Nevertheless there was one variety of the California dewberry, called the Aughinbaugh, which had been under cultivation for several years. This was the one selected for most of my experiments in hybridizing the dewberry; and this plant had a share in the production not only of the Primus berry, but of the even more remarkable Phenomenal berry to which reference will be made in a moment.

The cross between the Siberian berry and the California dewberry, from which the Primus sprang, was made without particular difficulty. I had learned by this time that blackberries and raspberries and dewberries could be hybridized almost indiscriminately; and the fact that one of the parents in the present combination had grown originally in Siberia and the other in California offered no barrier to the union.

With the first lot of seedlings, five hundred or more, from this union of the California dewberry and the Siberian raspberry, some strange specimens were revealed.

A Natural Hybrid
This natural hybrid raspberry was found growing wild by Mr. Burbank in Alberta, Canada. It was brought to Santa Rosa, and has been used in various hybridizing experiments. The chief interest of the plant, however, is that it is a natural hybrid that was growing in a stale of nature, and apparently competing successfully with both of its parents.

Nearly all were worthless plants, some of which seemed hardly to have vitality enough to live, much less to produce fruit. Others bore small, unattractive berries, insignificant in every respect. Three or four individuals, however, grew with unusual vigor. They differed so widely from the others that I was at first inclined to suspect that they were dewberries unhybridized. As to this, however, I was in error.

One of these exceptional vines was particularly notable. It neither trailed nor stood upright, but took an intermediate position. The leaves were not palmate like those of the raspberry, nor were they like the foliage of the dewberry. They were a compromise between the two.

The fruit, which was larger than that of either parent, resembled the blackberry most in form, but was of a dark mulberry color.

When the fruit was just ripe it parted from the stem like the blackberry; but when fully mature the core came out as it does in the raspberry.

Thus the combination of all these important characteristics was almost absolutely complete. The hybrid was a perfect blend.

It was this plant that was christened the Primus berry.

Seedlings by the thousand were raised from this selected hybrid and all of them came as true as the seeds of any wild species of the family. The offspring closely resembled the Primus, but none of them quite equaled it in fruiting qualities.

If found growing wild, the original Primus plant and its progeny would be pronounced by any botanist a distinct species.

The explanation of the summary production of a hybrid differing in this remarkable manner from either parent and being so fixed in type as to breed true to the new form thus suddenly developed would seem to be that the two parent species were separated almost to the limits of affinity. The fact that most of the hybrids of the same generation with the Primus were feeble and degenerate creatures is corroborative. It appeared, however, that there were elements in the two types of germ plasm that if combined in just the right way would produce a virile offspring.

By chance the right combination was effected, and the Primus berry was the result.

The berry itself has not proved a great commercial success, but that is a matter of small importance. The real importance of the experiment was in what it proved as to the possibility of the production of new species through hybridization. This was, in short, one of the first instances to come under my observation of the production of a hybrid that blends the characteristics of the parents, producing a new type and breeding true to that type.

To my mind—and I think the facts are convincing to any unprejudiced mind—this and many similar experiments that have been successfully accomplished demonstrates beyond dispute that hybridization is one of nature's methods of creating new species.

I have dwelt at length on this subject in earlier chapters. I revert to it here because of the importance of the subject itself, and also because the Primus berry furnishes us a new and striking illustration of the truth of the principle.

Of course the Primus berry was produced by artificial pollenizing of the plants that were so located geographically that they would have had no chance to hybridize unless brought together by man. But my observations show that natural hybrids are not at all unusual among wild members of this family. I have met with them often where two or three closely related species were growing side by side.

Near Lake Sycamour, for example, at Alberta, Canada, I have observed two common raspberries, Rubus leucodermus, a red raspberry, and Rubus strigosus, a black-cap, growing in close proximity around the hillsides and along the streams.

In every case where I found these two species growing together there were numerous natural hybrids in evidence. None of these hybrids were as productive as the parents, but the vines were usually stronger growers than either, and appeared to be hard pressing both parent species, with the prospect that they would in time supplant them in this region. I gathered large quantities of seeds from the best of these hybrids and brought them home for planting. Many seedlings were thus raised which obviously carried the combined characters of both their wild parents.

These representatives of a new species developed by hybridization under natural conditions have obvious scientific interest even though they failed to develop sufficient productivity to be of commercial value.

Let me repeat that natural hybrids are much more numerous than is generally supposed.

I have found them among other wild plants. Especially are they to be observed among strawberries, blueberries, huckleberries and California lilacs (Ceanothus). I have elsewhere cited instances of the hybridization of the tar-weeds and the mints. There can be no doubt that some of our well-known species of to-day were produced by Nature in this way within recent times.

I have elsewhere observed, and I emphatically repeat, that any theory of the origin of species that does not recognize this among the methods employed by Nature for the production of new species is altogether inadequate.


The result of thus mating the dewberry with the little raspberry from an almost Arctic climate having proved so remarkable, almost numberless tests were made in which the dewberry was crossed with a great variety of other raspberries and blackberries.

And among the hybrids thus produced there was at least one that might be considered more remarkable even than the Primus berry.

This was the fruit which afterward became famous as the Phenomenal berry.

This extraordinary berry was the outcome of a series of experiments in which the red and yellow raspberries were variously combined with the dewberry.

In the first generation of these hybrids, numerous red berries and black berries were produced, but no yellow ones. A large proportion of the red varieties followed the raspberry in general characteristics except in form, but some of them acquired the high flavor of the dewberry combined with the aroma of the raspberry.

The Phenomenal Berry
This also is a new species introduced by hybridization. Its parents were the California dewberry and the Cuthbert raspberry. Unlike the Primus berry, it is not a first-generation hybrid. It appeared in the second generation. The name "Phenomenal" is fully justified both because of the origin of the plant, and because it bears fruit that is perhaps larger than any other berry hitherto seen.

Most of the seedlings of this first generation resemble the wild dewberry in habit of trailing along the ground. Yet there were some that favored the raspberry, standing upright. In flavor many were a good combination of the two parents, but the variation was pronounced in this respect. Some were highly flavored while others were quite insipid, and between the two were all gradations. Variations in size and shape were equally marked.

Most of these seedlings were quite productive, but no one plant was sufficiently valuable to warrant its introduction as a new variety worthy of cultivation.

Berries were gathered, however, from the most promising of the dewberry-raspberry hybrids. Among the second-generation seedlings thus produced was one that was of different caliber from all the rest as shown by the character of its fruit.

No such berries were perhaps ever seen before as those that grew on this second-generation offspring of the Cuthbert raspberry and the California dewberry.

Some of the berries were an inch and a half long and an inch in diameter. They were a dark rich crimson color, slightly downy, and glossy. In flavor they combined the qualities of raspberry and blackberry, both flavors seeming to be intensified. In a word the fruit was a blend between the fruits of the parent races. It was a new variety so markedly distinct from either parent as to justify the designation of a new species.

The Phenomenal Berry
The color print shows this remarkable berry much reduced in size. Many of the berries are an inch and a half long and an inch In diameter. In flavor the Phenomenal berry combines the qualities of raspberry and blackberry, both flavors seeming to be intensified. Its individual qualities are so marked and distinctive that ills entitled to be designated a new species.

The new berry was originally called the Humboldt, but was subsequently rechristened the Phenomenal by the purchaser.

The new fruit was not altogether unlike the Loganberry, which was an accidental hybrid discovered by Judge J. H. Logan on his place near Santa Cruz, which was believed to be a hybrid between the red raspberry and the California dewberry. But the Phenomenal is far superior in size, quality, color, and productivity, and it is gradually displacing the Loganberry.

Unfortunately the two are sometimes confounded, and unscrupulous dealers have been known to sell the Loganberry under the name Phenomenal.

The new fruit, like most other plant developments—the Burbank plum, the Wickson plum, and the Pineapple quince, for example—was not fully appreciated for about ten years. But it is now a standard berry on the Pacific Coast, and as far as possible it is being introduced in other regions wherever it will thrive. As already noted, it is probably the largest of all known berries. As a fruit for drying and canning it is of the first importance.

From the standpoint of the plant developer the Phenomenal is of additional interest because of its almost exact combination or blend of the qualities of its parents.

I have raised numerous seedlings from the Phenomenal, but up to the present have found none that quite equals it in all its excellent qualities, though, like the Primus, it is a fixed new species, the seedlings not reverting to either parent form. The new berry has also been used as seed parent in a number of crosses with other blackberries and raspberries.

Some thousands of seedlings thus produced are now under observation.

Among these hybrids great variations will of course, occur, and while nearly all will undoubtedly be of inferior quality, I have confidently expected to find at least one that surpasses even the Phenomenal; and now this expectation has been fully realized in a new sweet variety which will later be introduced.


Hybridizing experiments of almost equal interest, even if not quite so striking in results, have been made between the various raspberries and the Lawton blackberry.

The Lawton is a very prepotent parent in these crosses, and its characteristics will almost invariably be found to predominate. Even the pollen of the Lawton when applied to the raspberry more often produces the Lawton type of berry than any other type. But in exceptional instances I have produced Lawton hybrids in which the prepotency was not so strongly manifested.

Such was the case, for example, with a cross between a yellow raspberry known as the Golden Queen and the Lawton. This produced a hybrid so well-balanced that no one who saw it could tell whether it was a raspberry or a blackberry.

Numerous seedlings of this hybrid strain were raised, and in the second generation the qualities of the hybrid were reproduced, as in the case of the Primus berry and the Phenomenal. No variation occurred such as is usual in the second generation of most hybrid blackberries and raspberries.

The bushes had prickles that were short and stout instead of long and slender as in the raspberry. The leaves also had the rough, ribbed appearance of the blackberry.

The berries would cling to the receptacle (a blackberry trait), or part from it (a raspberry trait), according to ripeness. As to color, there were both red and yellow varieties among the hybrid plants. The flavor of the berries was not exceptional, but in some other similar crosses made at a later period the fruit was in some cases greatly superior in quality to that of either of the parents.

Hawaiian Raspberries
This interesting berry is of very good quality, but does not last long enough for market purposes. Mr. Burbank is using this plant for hybridizing experiments. The experiments are still under way, and give promise of very interesting and perhaps important results.

Still greater interest attaches, perhaps, to a hybridizing experiment in which the parents were Shaffer's Colossal raspberry and the Crystal White blackberry.

Some of the plants from this cross were of the most tree-like proportions. Most of them, however, were barren, though they bloomed freely. But there were exceptional ones that fruited, and selected seedlings were grown from these through a series of generations. In the fourth generation a plant appeared which was of such extraordinary characteristics that it was given the name of Paradox.

This plant was in all respects a most perfect combination of the two ancestral forms from which it sprang. The wood, bark, leaves, blossoms, prickles, roots, and seeds could not by any test be proved to be like one or the other. The fruit, produced in abundance, was an oval, light red berry of good size, larger than that of either progenitor, and of fair quality.

Many of the first generation descendants of the Paradox were partially barren, though blooming freely. Sterility as to fruit was often associated with gigantic growth.

An Alaskan Raspberry
This Alaskan berry has qualities that entitle it to consideration on its own behalf, at least in the region where it is native. Mr. Burbank is using it in hybridizing experiments, and his success with the Siberian raspberry and other types of wild fruit leads him to think that interesting developments will result from the combination of the Alaskan berry with other races.

But some of the seedlings were fertile, and they manifested almost every possible combination of qualities of the raspberry and blackberry. Some were similar to the Paradox, except that they had white berries instead of red.

By saving seeds from the white and the red varieties separately, I found that they bred true, each constituting practically a fixed species.

As to the vines themselves, there is very little variation, the canes and foliage presenting an exact balance between the raspberry and the blackberry.

The berries are not of great commercial value, as the fruit though large is soft. I hope, however, to harden the berry by selective breeding, and introduce a better flavor.

Although this hybrid progeny of raspberry and white blackberry may ultimately have commercial importance, it is chiefly prized for the scientific significance of its revelations.

Descended as it is from a cross between the raspberry and the blackberry, it constitutes a fixed species differing radically from every other Rubus known.

So in this regard the Paradox takes its place besides the Primus and the Phenomenal berries as offering an impressive object lesson in the production of new species by hybridization. Let it be recalled, however, that the Primus was a first generation hybrid, whereas the Phenomenal appeared in the second generation, and the Paradox in the fourth.

An Interesting Hybrid
The fruit here shown is a cross between the yellow Golden Queen raspberry and the Lawton blackberry. It possesses qualities of both blackberry and raspberry.
    When blackberry-raspberry hybrids are picked, it is not unusual for them to bring away the receptacle with the fruit, like a blackberry, if they are not quite ripe; and to leave the receptacle, like a raspberry, if entirely ripe. Few of Mr. Burbank's experiments have greater scientific interest than those in which the raspberry and blackberry have been hybridized.

There has been occasion in an earlier chapter to tell of hybridizing experiments in some respects even more curious, in which the raspberry was fertilized with pollen of the strawberry. These experiments will be further examined in a later chapter, with reference to the interpretation of the observed phenomena of hybridization of the various brambles.

But perhaps no comment could greatly add to the impressiveness of the simple recital of facts as to the production of new forms that, according to all botanical standards, should rank as distinct fixed species, through the purposeful blending, under the hand of the plant developer, of the germinal strains of the various blackberries and raspberries.

—The chances of obtaining results in plant improvement are directly proportionate to the number of
experiments tried; and a hundred thousand experiments may be conducted as simply as a few.