In Dr. Denny's very interesting paper, read at the Birmingham Congress, "On the Relative Influence of Parentage in Flowering Plants," I find the following statement:—
"If we could by observation of results, acquired through the medium of a series of carefully performed experiments in artificial fertilisation, obtain any reliable evidence indicative of the relative influence the male and the female parents bear in the production of their progeny, it would assist us immensely in carrying out our designs for the improvement in the form and colour of our flowers, &c."
This is certainly a branch of knowledge which it is very desirable to possess, and it is probable that only by the recorded results of carefully performed experiments, anything approaching to this desired information will be obtained. The result, however, of my own experiments gives me but faint hopes of arriving at anything like certainty in the matter, although I have generally found that the progeny of two dissimilar plants of the same genus inherit the properties, more or less, of both parents; but this has never been so decided and obvious as to enable any one to predict with certainty as to which of the parents was most likely to prove prepotent, or most decidedly to stamp its peculiarities, as regards colour of flower, form, or habit of growth, upon the progeny.
One circumstance, however, has been so evident as to call for marked attention, viz., that in endeavouring to produce Variegated or Tricolor Pelargoniums, and using for this purpose plants with variegated and others with green foliage (as it is vain to hope for success by breeding from two variegated varieties), and where a green leaved sort is made the mother or the seed-bearer, the pollen being furnished by a variegated variety—the percentage of variegated seedlings so produced, though fewer in number, will generally be found to be in all respects superior to those produced by a variegated mother, both as regards constitutional vigour and beauty of foliage. I have, however, known some few exceptions to this rule (if I may so call it), viz., instances where a variegated seed-bearer has produced vigorous and well marked progeny, and instances have also occurred where seedlings so produced have greatly improved in vigour after having been increased by cuttings during several years.
I may here allude to an apparent sympathy existing between flowers and foliage, or rather to an antipathy or incompatibility between white flowers and yellow or golden margined foliage. It will be recollected that the best of the white flowered varieties of the Zonal Pelargonium are all vigorous growers, such as Madame Vaucher, White Perfection, and Mrs. Sach, and by fertilising these sorts with some of the best white margined or silver variegated kinds with red or pink flowers, such as Bijou or Silver Chain, varieties of tolerably robust habit of growth, with silver variegated foliage and pure white flowers, are to be obtained in the second or third generation; and by using as pollen parents some of the most robust and strong growing varieties of golden Tricolors, with white Zonals as seed bearers, I have been successful in obtaining golden Tricolor sorts with pure white flowers. But this has invariably been accomplished at the expense of constitutional vigour, as all varieties so produced have been so exceedingly weak, or what gardeners call miffy, that although very pretty they can with difficulty be kept alive.
Why this debility should be the invariable accompaniment of white flowers and yellow margined foliage, and not of white flowers and silver or white margined leaves, I confess myself unable to understand, and yet this I have always found to be the case. I have said that it is vain to try to breed from two variegated plants, as if this be done excessive weakness in the offspring will be found to be the unvarying result, variegation being always found to be accompanied by more or less diminution of vigour. And it is also found in the vegetable as well as in the animal kingdom, that in cases where both parents are predisposed to any peculiarity, that peculiarity is almost sure to be intensified in the case of the offspring. As an instance of this I may mention that some few years since such a thing as a double Petunia had not been heard of, when a double or rather a semi-double variety accidentally made its appearance amongst a batch of seedlings somewhere on the Continent, and was duly introduced to this country under the name of Imperialis. The colour of this flower was white, the plant was of straggling habit, and as a double flower it possessed but little merit. Previous to the introduction of this variety, some purple-flowered sorts were in cultivation, having exceedingly large flabby flowers; and in one of these—its name I do not now recollect—the flower contained a sort of inner corolla or small cup in the centre of the flower, somewhat resembling that of the Narcissus Poeticus, or Pheasant's-eye Narcissus. This was evidently a slight, but only a very slight approximation to duplication. The ovary of the variety producing white flowers being in an abnormal condition could consequently produce no seed, but anthers furnished with pollen were found among the petals of the flowers, and with this I fertilised some few blooms of the large purple flowered variety, and the result was a batch of seedlings of immense size, and many of them double as Roses, and varying in colour from pure white to dark purple—one of which, a white variety, was distributed under the name of Antigone, while a dark purple sort was named General Havelock, and as double flowered varieties they have probably not been surpassed even up to the present time. About this time there also existed several varieties of Petunias bearing single striped flowers, also some purple sorts in which the blooms were beautifully margined with a bright green edge, but showing no inclination whatever to duplication. Blooms of these various varieties I also fertilised with pollen of the double white Continental variety; and the result in this case was many single-flowered sorts of various colours, and a few semi-double striped and green-edged sorts. I selected the best of these, and, finding the ovary to be in a perfect and normal condition, during the following season fertilised them with the pollen of such sorts as General Havelock and Antigone, and was rewarded with many fine varieties with large double striped and green-margined flowers. It will be seen that, where the tendency to become double existed only in the case of one of the parents, it required two generations to arrive at the same degree of duplication that had been attained in one in the former instance, where the parents were both more or less predisposed to that condition.
It will also be observed by the above narrated experiments that the dark purple-flowered variety, when fertilised by the pollen of the double white Continental sort, produced varieties with double white as well as with double purple flowers. So that, as regards both colour and form, the male parent was in some instances prepotent, while the female was so in others, while the tendency to duplication inherent in both parents was strikingly intensified in the progeny. The result of the foregoing experiments gives, I think, no clue whatever to the discovery of any existing laws regulating the matter of prepotency, &c. Still, the acquisition of this, or of any other useful knowledge pertaining to the matter of hybridity, or crossbreeding, is very much to be desired, as irrespective of the valuable results which are continually being secured by this agency, in the form of improvement in the character and quality of our fruits, flowers, and vegetables, and cereals of all kinds, there are probably few pursuits connected with horticultural science more intensely interesting than that of being instrumental in the production of new and improved races of useful and ornamental plants.
But there must of necessity always be considerable uncertainty in the matter. And to altogether remove this uncertainty (supposing this to be possible) might in reality be undesirable, as it would as regards many minds divest the pursuit of a great portion of its charms. The pleasure of anticipation is said to frequently exceed that of realisation; and to anxiously watch the gradual development of organisms in the shape of new varieties of fruits and flowers, &c, which did not previously exist, and which owe their existence to one's own exertions, tends to create an absorbing degree of interest, and affords an amount of quiet pleasure which may be understood by even those who may not have as yet had practical experience in the matter. P. Grieve, Culford.