IN THE tropics: III. 105 



ripening apparently undergo a check prior to the formation of 

 starch, and the final product is of a sugary as opposed to a 

 starchy character. The grain on drying shrinks considerably 

 so that its surface is thrown into folds, and this fact affords a 

 visible external distinction by which the two types of grain 

 may be separated. It must be remembered, however, that 

 the fundamental distinction is a chemical one. In crosses 

 where the starchy (round) parent shows a very hard hyaline 

 endosperm, grains may occasionally be seen in F^, which 

 are intermediate between the typical round and wrinkled 

 kinds. In such cases there is no evidence that the chemical 

 difference does not still hold good, and the grains can always 

 be distinguished with certainty if their offspring are examined. 



2. Indentation as opposed to roundness. — Plants bearing 

 the former character produce elongated srains, the skins of 

 which are folded inwards at the extremity instead of being 

 convex. This difference appears to depend partly upon what 

 Correns calls the physical nature of the endosperm, but partly 

 also upon the characteristic shape assumed by the pericarp— 

 for the characters behave as if they belong to the parent 

 plants and not to individual grains. With regard to the 

 former point, the indented type of grain contains a larger 

 proportion of the loose floury inner endosperm as compared 

 with the amount of the hyaline substance which occupies 

 the more external region. According to my observations, 

 however, the relative amount of loose material seem to 

 increase with the size of the grain as we pass from the small 

 "pop corns," which are almost entirely hyaline, to the large 

 Cuzco, which is almost entirely starchy, and even upon the 

 same plant it may be observed that the larger lower grains 

 of a cob are more floury than the smaller upper ones. 



The above were the only characters with which it was found 

 possible to deal on a large scale. Such characters as size, 

 whether of grain, cob, or plant, were too indefinite or re- 

 quired too much time for their full determination to allow of 

 their use on the large statistical scale proposed. 



