230 



COMPENDIUM OF GENERAL BOTANY. 



made upon cryptogams it is assumed that among phanerogams 

 the nuclear substance (nuclein) of the pollen-tube enters the embryo- 

 sac and unites with the contents of the egg-cell. As a result the 

 egg-cell begins to develop into the embryo. The literature on 

 embryology is already very extensive. Special embryology has 

 succeeded in explaining many of the observed phenomena and 

 structures. The presence or absence of the suspensor, the behavior 

 of the antipodes, the formation of nutritive substances in the em- 

 bryo-sac (endosperm) as well as on the outside (perisperm), have 

 already been explained, in part very clearly and in part only hy- 

 pothetically. They evidently serve important functions in the 

 processes of growth in the embryo as well as in the young seedling. 

 For example, the suspensor, which is a simple cell-thread, assists 

 in placing the embryo in that position within the embryo-sac at 

 which the supply of nutrition is most favorable. According to 

 TREUB'S investigations, the suspensor of Herminium Monorchis 

 has the power of forming protuberances along the placentae. HOF- 

 MEISTER considered the endosperm as an enormously developed 

 suspensor. ' 



In regard to the development of the embryo of Capsella (Fig. 

 160), it should be stated that among dicotyledons the embryo nor- 



mally forms a depression at the 

 stem-apex between the two coty- 

 ledons (<?), while among the 

 monocotyledons (Alisma) the 

 elongated body of the embryo 

 is a lateral development of the 

 stem- apex instead of a terminal, 

 as in the foregoing. Other vari- 

 ations also appear among mono- 

 cotyledons : the originally ter- 

 minal apex may later be crowded 



FiG.m-Successive stages in the de- to One side ^ the Cot 7 ledo11 - 



velopment of a dicotyledonous plant, Among dicotyledons there are 



Capsella bursa pastoris. (Diagramatic.) , . M . ,. ,, ~ 



The dotted line in I represents the wall of the ^SO deviations from the Cap- 



sella-type of embryonal develop- 



stem, c cotyledons. 



ment. 



The suspensor is finally removed and replaced by the de- 



See also L. GUIGNARD, Ann. d. sc. nat., Ser. VI, T. XII, 1881. 



