EEPRODUCTION OF GTMNOSPEKMIA. 757 



pyle of the ovule, the primary embryo-sac, (b,) is developed in 

 the nucleus. This embryo-sac is at first very small (Jig. 11 09, b), 

 but gradually enlarges (Jig. 1110, a), and after a long period, 

 becomes filled with delicate cells, called endosperm cells 



1109. Fig.UlO. 



Fig. 1109. Vertical section of the yotingunimpregnated oviile of a species of 

 Finus. a. Nucleus containing a small primary embryo-sac, b. m. Micro- 



pyle, which is here very large Fig. 1110. Vertical section of an older 



ovule of a species of Pi'/iits. a. Enlarged primary embryo-sac. h. Eudo- 

 spermal cells withia the embryo-sac. c. rollen-tubes penetrating the 

 apex of the nucleus. 



{fig. 1110, h). The subsequent development of the ovule, and 

 the mode by which it is fertilized, is taken from Henfrey, and is 

 founded upon Hofmeister's investigations. 



"In the upper part of the mass of endosperm (Jig. 1110, h), 

 from five to eight cells are found to expand more than the rest, 

 forming secondary embryo-sacs. These are not formed in the 

 superficial cells of i, but from cells of the second layer, so that 

 each is separated from the membrane of the primai y embryo-sac 

 by one cell {fg. 1 111, a). Those cells lying between the secon- 

 dary embryo-sacs and the surface of the endosperm, next under- 

 go division cross-wise, so as to form a rosette of four cells, 

 which separate at the converging angles, and leave a central 

 intercellular passage down to the secondary embryo-sac 

 {fig. 1111, b). In this state, these corpuscula, as they were 

 called by R. Brown, their discoverer, are very much like the 

 archegonia in the internal prothallium-structure of Selaginella 

 (Lycopodiace^e, p. 7.53, and^^. 1105)." 



The process of fertilization takes place as follows : — " The 

 pollen-grains fall at once upon the ovules and pass into the 

 micropyle, (sending down their pollen-tubes here developed 

 from the internal cellular body, which passes out through the 

 proper coat of the pollen-cell,) through the substance of the 

 upper part of the nucleus {fig. 1110, c), and reach the mouth 

 of the canals of the corpuscula, one entering each {fig. 1111, 

 B, pt). At the same time, germinal corpuscles are produced at the 

 3 c 4 



