THE EMBRYO 



195 



Corallorhiza multiflora, in which it consists of two very long- 

 cells and embeds its tip into the placenta; of Habenaria tri- 

 dentata, and of II. blephariglottis, in which each of the six or 

 seven cells of the snspensor usually sends out a branch, some of 

 them short and reaching the integument, others elongated and 

 passing parallel with the suspensor into the tissue at the base 

 of the funiculus. 



These four types of monocotyledonous embryos, which for 

 convenience may be spoken of as Alisma, Pistia, Lilium, and 

 Orchid types, are, of course, related to one another in ways that 

 suggest that they are all derivatives of one general monocotyled- 

 onous form. It is natural to assume that this primitive form 

 is more nearly represented by the Alisma type than by any of 



B 



Fig. 88. — Zannichellia palustris. Development of embryo. A, young embryo ; x 320; 

 B, later stage, showing beginning of differentiation into stem-tip (*) and cotyledon (c), 

 both coming from the cells derived from terminal cell of proembryo ; x- 160 ; C\ stem- 

 tip (s) and cotyledon (c) clearly differentiated ; x 60. — After Campbell. 41 



the others, not merely because it characterizes the primitive 

 hydrophytic forms, but also because it is the simplest type, 

 and the others may well be modifications of it. In the Pistia 

 type the suspensor is suppressed ; in the Lilium type it becomes 

 massive and meristematic ; in the Orchid type it is developed 

 as a special haustorium that passes out of the ovule on account 

 of the lack of endosperm, and perhaps for the same reason the 

 embryo does not reach the stage of differentiating organs. 



There have been observed certain departures from the mon- 

 ocotyledonous type of embryo that deserve special mention. 



