266 shuii. 



the fact that the heterozygote has the successful parental type and 

 can preserve the less successful new form for an indefinite number 

 of generations until a situation may arise in which it can become a 

 success. Thus, although the gardeners have regularly sown seeds 

 only of the normal type of Digitalis purpurea, the heptandra-ioxva 

 has probably been kept potentially in existence for more than three- 

 quarters of a century until it found, for a few years at least, an en- 

 vironment adapted to its successful existence, — in the gardens of 

 the geneticists. 



Legends for figures. 



All flowers figured in Plate XV are viewed from the ventral side 

 and drawn to the same scale. With exception of Figs. A and B, all 

 were drawn from nature by MR. Kako Morita. The lettering follows 

 that of DE ChamissO'S figures, two of which are reproduced here as 

 Figs. A and B. As none of de Chamisso's figures show the posterior 

 pair of accessory stamens, these are labeled here p, p, k, k, i, i = normal 

 stamens; p, p, h, h, g = accessory stamens; e, f, f, i, i = segments of "acces- 

 sory corolla". 



Fig. A. Drawn from a tracing of de Chamisso's fig. 2, showing seven stamens 

 and the five lobes of the accessory corolla, the "lacinulae corollinae", all distinct 

 and equal. 



Fig. B. Drawn from a tracing of de Chamisso's fig. 3. The three accessory 

 stamens, h, h, and g, are severally united with adjacent normal stamens, 1, 1, and k. 

 Posterior lateral lobes, f, f, of the accessory corolla relatively long. 



Fig. I. A normal corolla of Digitalis purpurea L. Ventral lip longer than the 

 dorsal. Treated as a transparency to show the normal position of the stamens. 



Fig. 2. A low-grade heptandra flower; the ventral lip considerably shortened, 

 the three accessory stamens, h. h, and g, appearing as imperfectly developed anthers 

 on the margin of the corolla. The lobes of the accessory corolla are also fore-shadowed. 



Fig. 3. A very common hcptandra-type with seven free stamens and only the 

 ventral lobes, i, i, of the accessory corolla apparent, the dorsal lip of the corolla 

 remaining almost entire. 



Fig. 4. A similar form in which the dialysis of the corolla is less complete, the 

 ventral lobes of the accessory corolla not apparent because they remain united with 

 the ventral accessory stamen, g. The lateral accessory stamens, h, h, are also partially 

 united with the dorsal lip of the corolla. 



Fig. 5. A similar flower in which the ventral lobes, i, i, of the accessory rorolla 

 are partially free from the accessory stamen, g, and in which the configuration of the 

 dorsal lip of the corolla foreshadows the two dorsal accessory stamens, p, p, and the 

 "lateral wings", f, f, of the accessory corolla. 



Fig. 6. All parts of both accessory androecium and accessory corolla are clearly 

 present, but the posterior accessory stamens, p, p, are club-shaped and yellowish, 

 showing no other indication of antherformation. 



