104 



MORniOLOGY OF SPERM ATOPUYTES 



oinneiit of enibrTos. At the end of a single suspensor two 

 enil)Vvos liad liesiiin to develoii, the lirst division of tlie em- 

 bryonal cell having been longitudinal, and the two daughter 



cells having become so organicallr 

 dissociated that they pursued their 

 further history independently. 

 The eml>ryo may thus start with 

 a plate of ('ells or with a single 

 cell, and hence there is probaljly 

 no A-ery definite seipience of 

 events. In the case of embryos 

 which develop from a single cell, 

 the tirst two or three divisions are 

 usually transverse (Fig. 78), al- 

 thougli cases have bt'cn found in 

 wliicli the first wall is vertical. 

 Whether there is any detinite 

 sequence of events or not between 

 these carlv stages of the embryo 

 and the organization of its great 

 regions (Fig. Tit) is uncertain, but 

 it is probable that the behavior 

 of these primitive cells may be 

 exceedingly variable, dependent 

 upon conditions which have not 

 yet been recognized. 



The current statements as to 

 the strTicture of the root and stem 

 liecn derived mainly from Stras- 

 burger.^" In reference to the root tip this author states that in 

 Gymnosperms in general the differentiation of meristom at the 

 apex of the root is essentially different from that of Angio- 

 sperms. A full statement of the difference was given under 

 the root. The differentiation of the regions at the apex of 

 the stem shows consi<lerab]e variation in (iymnosperms. As 

 was reiiiarlvcil under the stem, in Ihi in iiiarci, (' u iiiniKjliainta, 

 and certain s]n'ries ol A ra iii-((riii , tlie dermatogi'U, jieriblem, 

 anil ]i]<'rome are ldear]^• distinguishable at the V(.'rv apex; while 

 in the Abieteac the three regions merge in a counnon group 

 of initials, a character shared by the Cycads. It is interesting 



I'm. Ya. — /'iiuis I.(iri,-in, a fully 

 vclopeJ embryo imbet.ldeJ in the 

 eudosperni. 



tijis of Gynmosperi 



us 



have 



