498 BOTANICAL GAZETTE [DECEMBER 
restated the conclusions previously arrived at from a study”™ of A gapanthus 
umbellatus and some other monocotyls as follows: ‘In the embryogeny of 
oth monocotyledons and dicotyledons, a peripheral cotyledonary zone gives 
rise to two or more growing points, or primordia; this is followed by zonal 
development, resulting in a cotyledonary ring or sheath of varying length. If 
both growing points continue to develop equally, the dicotyledonous condition 
is attained; if one of the growing points ceases to develop, the continued 
growth of the whole cotyledonary zone is associated with that of the other 
growing point, and the monocotyledonous condition is attained. In like 
manner, polycotyledony is simply the appearance and continued development 
of more than two growing points on the cotyledonary ring. It follows that 
cotyledons are always lateral a” arising from the peripheral zone 
developed at the top of a more or less massive proembryo. This reduces 
cotyledony in general to a common basis in origin, the number of cotyledons 
ing a secondary feature. The constancy in the number of cotyledons in a 
great group is no more to be wondered at than the same constancy in the 
number of petals developed by the petaliferous zone.” . 
To those whose mental processes require a “type” for everything, the 
embryogeny of the grasses is very puzzling, because it does not conform to 
the hitherto accepted caibapicea? ds “type” of embryogeny. The structures 
have received the names “‘scutellum,” “epiblast,” and “coleoptile.”” Early in 
the history of the subject the scutellum was recognized as the cotyledon. The 
epiblast was recognized as a second and rudimentary cotyledon from its first 
discovery until the time of SCHLEIDEN, who in 1837 so clamorously dissented 
from this view that it was suppressed from the literature of the subject until 
1897, when VAN TIEGHEM, studying the embryogeny of grasses, reaffirmed that 
the epiblast is a second cotyledon. In the meantime HANsTEIN, followed by 
FAMINTZIN, had made a study of Alisma, which has a filamentous and therefore 
highly specialized proembryo, and fixed what has been almost universally 
regarded as the monocotyl “type” of embryo. Because of these first studies, 
the massive proembryo, so prevalent 1 in monoentyledors, sas = called the 
“‘aberrant type,”’ although it d generalized, 
while the filamentous proembryo is the more specialized. About two-thirds of 
the grasses show a well marked second cotyledon. This second cotyledon is 
quite pronounced in those grasses which have a relatively long internode 
(“mesocotyl”’ of English anatomists) between the cotyledons and the “‘coleop- 
tile” or bud-scale leaves. 
CoutterR shows that there is a progressive reduction of the second cotyle- 
don until Zea Mays is reached, where the only external sign of the second 
cotyledon is a small hump opposite the functional eae but even here a 
small procambium is present, being exactly opposite the procambium of the 
© COULTER, JoHN M., and Lanp, W. J. G., The origin of monocotyledony. Bor. 
Gaz. 57:509-519. pls. 28, 29. 1914. 
