A third example of partial gametic coupling relates again primarily to the blue factor (B) and the pollen-shapes, but in order to make clear the circumstances in which it occurs, another set of phenomena must first be described.
In the old types of Sweet Pea the standard is erect and has a small notch in the middle of its upper border. This is the natural shape of the wild flower. Of the modern types many are what is called "hooded." The standard in hooded forms turns forward and downward in various degrees, the amount varying with the type and also to some extent with the weather and the condition of the flower. The hooded standard differs also from the erect one in having little or no trace of the central notch. This difference causes the buds of the two types to be recognizably distinct before the flower opens, for in the hooded type the point of the folded standard projects sharply forward in front of the wings, while in the erect type this tip is rounded off by reason of the notch. (Plate V.)
The hooded standard also is sometimes distinguished by the existence of a sinus of variable size on each side of the standard, which thus has lateral lobes more or less well developed. These differences obviously point to a different distribution of the strains produced by the growth in the two types. The lateral sinus is not represented in the hooded flowers shown in Plate V.
|* Similarly if the bicolour purples with dark wings are present in the class with an erect standard, they are represented by "Duke of Sutherland" in the hooded class, viz. a deep unicolorous purple.|
The hooded types may have a great diversity of colours, and fixed hooded varieties now exist in the purple, blue, red, pink, cream and other classes. It is nevertheless a remarkable fact that, so far as I am aware, none of the regular bicolour varieties ever have a really hooded standard. There is for instance no hooded type having the colour of the original purple, with its chocolate-purple standard and blue wings, nor can Painted Lady with standard red and wings nearly white be produced in a hooded shape. On the contrary the hooded types always have the standard and wings more nearly alike in colour, and there is the clearest evidence that in families (F2 and later generations) which contain original bicolour purples as well as hooded types, the hooded types corresponding to them are of the unicolorous kind known as "Duke of Westminster*."
From these facts it is evident that there is here some interdependence between the colour of the flower and its form. This interdependence is of course somatic, but as will be seen there is also a gametic connection between the phenomena of shape and colour.
The experiments bearing on these questions originated in a cross between the white, round-pollened Emily Henderson and a white, long-pollened hooded type known as Blanche Burpee. The Emily Henderson has an ordinary erect standard with the central notch.
F1 produced from these two is a bicolour purple, with erect standard and long pollen, indistinguishable from the reversionary previously described as the offspring of the long and round whites. F2 from such plants consists of the following types:
Emily Henderson. 2. Blanche Burpee 3. Purple Invincible, F1.
4-11. The various F2 types obtained by self-fertilising F1. 4. Purple Invincible. 5. Duke of Westminster. 6. Painted Lady.
7-9. Corresponding dark winged types. 7. Purple, with purple wings. 8. Duke of Sutherland. 9. Miss Hunt. 10 and 11. F2 whites.
Notice that there is no hooded red.