INTRODUCTORY 7 



It is claimed that the prophyllum * of Monocotyledons is 

 solitary and posterior, while in Dicotyledons there are two op- 

 posite and lateral prophylla. If such structures generally 

 occurred, or even if this distinction were generally true when 

 they do occur, such a character would be significant, for the 

 prophyllum certainly has a definite connection with the position 

 of the successive floral parts in relation to the main axis. 



It has been urged also that the Monocotyledons are char- 

 acterized by a small embryo embedded in an abundant endo- 

 sperm, and that in Dicotyledons the tendency is to develop 

 larger embryos at the expense of the endosperm. This involves 

 so many and such important exceptions that it can hardly be 

 regarded as a distinction between these two great groups. 



The roots of Monocotyledons are said to differ from those 

 of Dicotyledons in that the primary roots are short-lived and 

 there is no persistent root-system as in many . Dicotyledons. 

 While this may be true of Monocotyledons in general, it is also 

 true of many Dicotyledons, and can not be used as a distinct- 

 ive character. 



All the characters enumerated above, both those of primary 

 and those of secondary importance, are to be considered in any 

 general characterization of the two groups; but it must be re- 

 membered that most of them await confirmation as essential 

 group characters. It is of interest to note that they are all 

 characters of the vegetative sporophyte, and that the sporangia 

 and gametophytes of Monocotyledons and Dicotyledons have 

 tlius far given no tangible evidence of group differences. 



* Translated into German as VorUatt, and into English as fore-leaf. The 

 first leaf on a branch, but used only in connection with the bractlets of a 

 flower cluster. 



