422 cook: seedling morphology 



and splits open on one side for the emergence of the plumule. 

 Thus the cotyledon itself, like all of the subsequent leaves of the 

 palms, has a sheathing base. 



After being planted by the elongated burrowing base or 

 petiole of the cotyledon, the palm embryo encounters the same 

 problem of pushing its way to the surface of the soil as does the 

 grass embryo, and has solved it in a similar way, by specializing 

 the lower joints of the plant axis. Instead of producing com- 

 plete, bladed leaves, the internodes immediately above the 

 cotyledons of palms and grasses produce only small, rudimen- 

 tary leaves, in the form of narrow, cylindrical bladeless sheaths. 



The germination of the maize plant shows the extent to which 

 these specializations have been carried in grasses. Even when 

 the seeds are buried under several inches of soil the bladeless 

 first leaf, or coleoptile, may be carried up to the surface by the 

 growth of a specially elongated root-bearing section of the axis. 

 The extreme cases are found in some of the varieties of maize 

 grown by the Hopi, Navajo, and other native Indian tribes of 

 the dry table-lands of New Mexico and Arizona. 3 



The more or less elongated section of the stem below the cole- 

 optile of the maize is called by some writers hypocotyl, by some 

 epicotyl, and by still others mesocotyl, the name depending upon 

 whether the organ was supposed to be a part of the cotyledon 

 or a distinct morphological element above or below the cotyledon. 

 Some others have looked upon the coleoptile as the cotyledon. 

 If both the scutellum and the coleoptile are considered as parts 

 of the cotyledon, the intervening structure has to be reckoned 

 likewise as a part of the cotyledon. On this basis, mesocotyl 

 would be the more appropriate term, and it may also be justified 

 on the ground that the coleoptile has analogy, if not homology, 

 with the cotyledons of other plants. 



A distinct name, mesocotyl or some other, is needed, because 

 this part of the axis, in producing roots along its entire length 

 instead of only at the upper end, is unlike the other internodes 

 and there are differences of internal structure. That the meso- 



8 Collins, G. N. A drought-resisting adaptation in the seedlings of Hopi 

 maize. Journ. Agr. Research, 1: 293-301. 1914. 



