I.V1 Itniil (HON. 



9 



depressions in these seeds were sometimes mere pitting, 

 as iii Victoria Marrow; or they maj be so marked that 

 ill, ml would bedea ribed as wrinkled. The latter were 

 especially common in William the First, but microscopic 

 examination showed at once that these Beeds are really 

 of the round type. There arc, 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 ean not at present he 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 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 wrinkling of the wrinkled 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 Darbisbire, 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 0.0323 nun. and an average breadth 

 of 0.0213 nun. The length-breadth-index (i.e., 100 X 



dth -f- length ) is 66.1 1. Besides these potato-shaped 

 grains, there are extremely lew 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 bei ween 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 1, .">. 

 or 6 components; grains with 7 or 8 are rarer; grains 

 with 2 or 3 are intermediate in frequency between those 

 with -1, 5, or on the one hand and 7 or 8 on the other 

 While the grains with 7 to 8 pieces are not much larger 

 than those with 1. ■">, or 6 : grains with 2 or 3 are always 

 conspicuously smaller than those with I, 5, or (',. 'The 

 average length is 0.0269 mm., the average breadth 

 ii.ii-.' is mm., and the length-breadth-indes 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 F, cotyledons produced by cros 

 the round witli the wrinkled pea are nearly round; the 

 majority of the grains are single and the remainder com- 

 pound; the compoundness exhibited by the compound 

 grains in F, seeds is intermediate between singleness and 

 i he degree of compoundness in the grains of wrinkled 



peas, foi lile in the latter the aum 



between 2 ami 8 aid the commom 



ii Mine- between 2 ami I and the con The 



differences in the measurements of thi 



shown in table '.', by which it will l»- seen that in 



the I', grain is intermediate between haped 



grain and the compound "/rain, but nearer the latter. 



Taui.i 2. 



Average* length 



Averuge breadth 



Length-bread th-indez 



Wrinkled. 

 compound 



gruin. 



0.0248 

 02.19 



Darbisbire also examined the grams of F.. '1 

 he did not measure, hut lie state- that no differences could 

 be seen between the potato-shaped, compound, and round 

 grains from the three type- already described. He 

 that the evidence points to the fact that the heterozygote 

 round peas in generations subsequenl to F, are charai 

 ized by the pos i ion of irregular round or round gram-, 

 and homozygote round peas by potato-shaped grains. 

 Darbishire records thai if the association of round grains 

 with heterozygote round and of potato-shaped grains with 

 homozygote round holds good for the F 2 generation, we 

 have a means of distinguishing between DD round and DR 

 round in F 3 , instead of, as at present, having to wait 

 until their progeny are mature in the following year. 

 Another point demonstrated by the nature of grains in 

 F„ and borne out by those of 1'.. is that the shape of 

 the grain is inherited separately from it- composition — 

 if we may use this term to cover the singleness or com- 

 poundness of the grain. In the round pea the grains are 

 single and long; in the wrinkled peas they are compound 

 and round; in the hybrid they may he either single or 

 compound, hut are more round than long. In 

 are round grains exhibiting much compoundness and 

 others exhibiting little. I' bl] there are poi ii 

 grains either with no compounds or with few, and inter- 

 mediate grains either with few compounds or with many. 

 The wrinkled peas of this generation contained, as was 

 to be i pound grains, but some of them had 



in addition, very sparingly potato-shaped grains. Dar- 

 bishire also studied the absorptive capacities of the three 

 starches in relation to water. The following facts 

 summed up from the results of his ii ms: 



1. Although roundness is dominant over vrinkled- 



h-grain of the F, generation 



is a blend between tin grain of the round pea 



(the potato-shaped) and 1 ain of the wrinkled 



pi i (tl e i and) in respect of three characters: 



it is intermediate in shape a- measured by its length- 

 breadth-index, that of the potal ain being 

 66.] I. that of the compound grains 92.19, and that of the 

 n. uml srrain 8.5; (6) it i- intermediate in the distribu- 



