THE ORIGIN OF MONOCOTYLEDONY 



II. Monocotyledony in Grasses 



J. M. COULTER 

 The University of Chicago 



Recently Dr. Land and I published 1 the results of an in- 

 vestigation suggested by a specimen of Agapanthus umbel- 

 latus, one of the South African Liliaceae, possessing two good 

 cotyledons. It seemed to us that if the seedlings of the same 

 species are indifferently monocotyledonous or dicotyledonous, 

 there must be some evident relationship between the two con- 

 ditions. These two conditions of the seedling of Agapanthus 

 were compared critically, and Sagittaria was included in the 

 investigation because it has stood, along with Alisma, for the 

 typical monocotyledonous embryogeny, in which the terminal 

 cell of a filamentous proembryo is said to give rise to the 

 single cotyledon, in contrast with the dicotyledonous embry- 

 ogeny, in which the corresponding terminal cell produces the 

 stem tip, and the cotyledons are distinctly lateral. No con- 

 trast would seem sharper and less capable of being confused 

 with intergrades. 



The result of the investigation, as recorded in the paper 

 referred to, was to show us that there are no such rigid cate- 

 gories for cotyledony; that the cotyledonary apparatus is al- 

 ways the same structure, arising in the same way, and vary- 

 ing only in the details of its final expression. Briefly stated, 

 the situation is as follows : In the embryogeny of both mono- 

 cotyledons 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 con- 



1 Coulter, John M., and Land, W. J. G. The origin of monocotyledony. 

 Bot. Gaz. 57:509-519. pi. 28-29. 1914. 



Ann. Mo. Bot. Gard., Vol. 2, 1915 



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