POSITION OF SCUTELLUM AND HOMOLOGY 



OF COLEOPTILE IN MAIZE 



(with eleven figures) 



Paul Weatherwax 



The homologies of the grass embryo and their bearing upon 

 ideas of the phylogenetic relationship of monocotyledonous and 

 dicotyledonous plants have been subjects of study and discussion 

 for a long time, and although most botanists are fairly well agreed 



* 



upon most phases of the question, some points are still subject to 

 controversy. It is realized that evidences drawn from a single 

 species as highly specialized as maize will not go far toward the 

 making or the breaking of a theory, but two things have been 

 observed in the structure and development of the embryo of Zea 

 Mays that seem to have a definite bearing upon the subject, and 

 these are offered for what they may be worth. 



The history of the subject has been fully reviewed, and certain 

 sharply contrasted opinions have been presented recently by 

 Worsdell and by Coulter and Land. Further reference to the 

 voluminous literature seems unnecessary here, and only those points 

 to which the information at hand is related will be considered. 



maintain 



^ 



embryo is a lateral organ, the equivalent of the foliage leaf. The 

 epiblast represents the cotyledon that was lost in the evolution 

 from the monocotyledonous condition, and the coleoptile is the 

 third leaf. Opposed to this is Worsdell's 2 contention that the 

 cotyledon, which he considers terminal in origin, is the lamina, and 

 the coleoptile is the ligule, of a single foliage leaf, whose sheath was 

 present only in early stages of development. The epiblast is said 

 to be the equivalent of the auricles of the foliage leaf. The princi- 

 pal evidences brought to the support of this view are the double 



1 Coulter, J. M., and Land, \Y. J. G., The origin of monocotyledony. II. 

 Monocotyledony in grasses. Ann. Mo. Bot. Gard. 2:175-183. 1915. 



2 Worsdell, W. C, The morphology of the monocotyledonous embryo and that 

 of the grass in particular. Ann. Botany 30: 509-524. 1916. 



179] 



[Botanical Gazettee, vol. 69 



