104: 



MORPHOLOGY OP SPERMATOPHYTES 



opment of embryos. At the end of a single suspensor two 

 embryos had begun to develop, the first division of the em- 

 bryonal cell having been longitudinal, and the two daughter 



cells having become so organically 

 dissociated that they pursued their 

 further history independently. 

 The embryo may thus start with 

 a plate of cells or with a single 

 cell, and hence there is probably 

 no very definite sequence of 

 events. In the case of embryos 

 which develop from a single cell, 

 the first two or three divisions are 

 usually transverse (Fig. 78), al- 

 though cases have been found in 

 which the first wall is vertical. 

 Whether there is any definite 

 sequence of events or not between 

 these early stages of the embryo 

 and the organization of its great 

 regions (Fig. 79) 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 structure of the root and stem 

 tips of Gymnosperms have been derived mainly from Stras- 

 burger. 17 In reference to the root tip this author states that in 

 Gymnosperms in general the differentiation of meristem 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 considerable variation in Gymnosperms. As 

 was remarked under the stem, in Dammara, Cunninghamia, 

 and certain species of Araucaria, the dermatogen, periblem, 

 and plerome are clearly distinguishable at the very apex; while 

 in the Abieteae the three regions merge in a common group 

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



FIG. 79. Pinus Laricio, a fully de- 

 veloped embryo imbedded in the 

 endosperm. 



