192 



MORPHOLOGY OF ANGIOSPERMS 



it we would cite Sparganium (Campbell 55 ), Potamogeton 

 (Wiegand, 63 Holferty 71 ), Z-annichellia and Naias (Camp- 

 bell 41 ), Triglochin (Hill 60 ), and Limnocharis (Hall 82 ). The 

 last-mentioned form well illustrates that the general type may 

 be maintained, and at the same time there may be no regularity 

 in the sequence of divisions after the first two. In fact, the 

 apical cell of the proembryo of Limnocharis may divide by a 

 transverse, oblique, or longitudinal wall, and in the two latter 

 cases the cotyledon and stem-tip are both terminal, as is the 

 case also in Zannicliellia. 



Among the Gramineae the same general type of proembryo 

 is formed, but if Avena fatua (Cannon 65 ) be taken as repre- 

 sentative of the general situation, the origin of the organs of 

 the embryo in relation to the cells of the proembryo is quite 

 different. In this species the cotyledon and stem-tip are both 

 derived from the apical cell, the entire root-tip (including root- 

 cap) from the adjacent cell, and the coleorhiza from the third 

 cell, the suspensor consisting of only the primary basal cell. 



Among the Araceae a very different type of embryo is indi- 

 cated, but so few forms have been investigated that no conclu- 

 sion as to its prevalence in the family is safe. In 1874 Hegel- 



maier 9 described the absence of 

 a suspensor in Pistia, the fertil- 

 ized egg producing a spherical 

 proembryo, all of which enters 

 into the structure of the embryo. 

 Campbell 59 found the same type 

 of embryo in Dieffenbachia, Ag- 

 laonema, and Lysichiton (Fig. 

 84), and states that in the seg- 

 mentation of the egg there may 

 be two transverse divisions be- 

 fore any vertical division, or a 

 regular quadrant may be formed 

 as in the ordinary fern embryo. 

 Even if this Pistia type should 

 prove to be characteristic of the 

 Araceae, it is not restricted to them, for Humphrey 38 has 

 shown that the embryos of the Scitamineae have no suspensors ; 

 and the same is true at least of certain orchids, as shown by 



FIG. 84. Lysichiton kamtschatcense. 

 Longitudinal section of embryo sur- 

 rounded by endosperm, illustrating 

 the Pistia type. After CAMPBELL." 



