128 BREEDING 



into starcli. This starcli is in the form of grains 

 which, in the case of the round pea, may be best 

 described as potato -shaped. They are shown in 

 Fig. 28. These grains can easily be seen, in the 

 following way : A dry round pea is soaked in water 

 for twenty- four hours ; a thin slice is then cut off 

 with a razor, the cut surface of the pea is then 

 wetted with a drop of water, and scraped. The 

 whitish fluid scraped off will be found to consist 

 almost entirely of these starch grains, when examined 

 through the microscope. 



If the starch grains of a wrinkled pea (Fig. 29) 

 are examined in the same way they will be found to 

 present a very different appearance from those of the 

 round pea, for whilst the latter are entire, the former 

 are compound ; their substance is subdivided by 

 radiating strands of a refringent yellow matter. More- 

 over, whilst the grains of a round pea are distinctly 

 elongate, those of a wrinkled one are roughly 

 circular, if we neglect the indentations caused by 

 the radiating strands. 



It is evident, then, that the starch is in a different 

 state in the round pea from that in which it occurs 

 in the wrinkled. The probable nature of this differ- 

 ence is indicated by the following experiment : If 

 a round pea is weighed, and then soaked in water 

 for twenty-four hours, and then weighed again, the 

 weight of water absorbed can be determined. If 

 this weight is then expressed as a fraction of the 

 weight of the dry pea, a certain figure, which I have 

 called the " absorptive capacity," is obtained. The 



