STARCII-GUAIN IN RELATION TO MENDELISM. 



73 



centers, thus forming a compound <yvMn which has a strong tendency to break up into 

 smaller parts In the cells which lie deeply these compound grains never attain a greater 

 length than 0.1 mm. in the greatest dimension. Table 3 gives a list of the seeds examined. 



Table 3. 



Gregory notes that seeds of intermediate and dubious shapes were not uncommon in 

 certain of the races. The depressions in these seeds were sometimes mere pitting, as in Vic- 

 toria Marrow ; or they may be so marked that the seed would be described as WTinkled. The 

 latter were especially common in William the First, but microscopic examination showed at 

 once that these seeds are really of the round type. There are, therefore, states Gregory, two 

 entirely different types of wrinkling, and while it is clear that the process by which wrinkling 

 is produced is connected with shrinkage on drying, the regularity of the shrinking of the 

 round type and its irregularity in the two other types can not at present be explained. There 

 occasionally occur among the offspring of hybrids between round and wrinkled types seeds 

 of dubious shape which it is difficult on superficial examination to classify as round or 

 wrinkled. The existence of such seeds and types of doubtful shape was taken by Weldon 

 (Biometrika, 1902, i, 246) to indicate irregularities of Mendelian segregation and dominance, 

 but Gregory states that no seed has been found which upon histological examination allowed 

 of any doubt as to its true character, and consequently that occasionally pitting and spurious 

 wrinkling must be distinguished from the true WTinkling of the w^rinkled types. 



The nature of the starch-grain in the hybrid, and how the characters of the starch- 

 grains segregate, if they do so at all, in subsequent generations, are points which suggested 

 themselves to Darbisliire (Proc. Roy. Soc, B. 1908, lxxx, 122), who states that they are 

 matters on which we are ignorant. He found that the starch-grains of the round pea, 

 such as of the "Eclipse," appear as single potato-shaped grains, with an average length of 

 0.0322 mm. and an average breadth of 0.0213 mm. The length-breadth-index {i.e., 100 X 

 breadth -^ length) is 66.14. Besides these potato-shaped grains, there are extremely few 

 very much smaller grains which are round. The grains of wrinkled peas like the "British 

 Queen" are compound, each consisting of a number of pieces which vary between 2 and 8. 

 These pieces are held together by a refrangent yellow substance which does not color 

 blue with iodine, and they are likely to break apart. The commonest types are those with 

 4, 5, or 6 components; grains with 7 or 8 are rarer; grains with 2 or 3 are intermediate in 

 frequency between those with 4, 5, or 6 on the one hand and 7 or 8 on the other. Wliile 

 the grains with 7 to 8 pieces are not much larger than those with 4, 5, or 6, grains with 

 2 or 3 are alwaj's conspicuously smaller than those with 4, 5, or 6. The average length is 

 0.0209 mm., the average breadth 0.0248 mm., and the length-breadth-index is 92.19. In 

 these peas are a number of very small single grains which can be distinguished from the 

 pieces of the compound grains by the fact of their being circular and always smaller than 

 the grains consisting of two pieces. Very rarely will be found isolated potato-shaped grains. 



The grains of the Fi cotyledons produced by crossing the round with the wrinkled 

 pea are nearly round; the majority of the grains are single and the remainder compound; 

 the compoundness exhibited by the compound grains in Fi seeds is intermediate between 



