774 



PHYSIOLOGY. 



{fig. 1117, a), enclosed by a single coat, and with a large mi- 

 cropyle, m. Before the contact of the pollen with the micro- 

 pyle, the primary embryo-sac (h) is developed in the nucleus. 

 This embryo-sac is at first very small {fig. 1117, h), but gra- 

 dually enlarges {fig. 1118, a), and after a long period, becomes 

 filled with delicate cells, called endosperm cells {fig, 1118, b). 

 The following account of 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 {fig. 1118, 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 b, biit from cells of the second layer, so that 

 each is separated from the membrane of the primary embryo-sac 

 by one cell {fig. 1119, a). Those cells lying between the secon- 

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

 go division crosswise, so as to form a rosette of fovir cells, 

 which separate at the converging angles, and leave a central 

 intercellular passage down to the secondary embryo-sac {fig. 

 1119, b). In this state, these corpuscida, as they were called by 



i^^V^. 1119. 



Fig. 1119. Developnient of the einljryo in a species of Pimis (Pinacese). 

 After Henfrey. A. Upper part of the embryo-sac, with two secondary 

 embryo-sacs, corpuscula, or arrhegonia. b. The same, more advanced. 

 J)^ Pollen-tube in the canal leading down to the corpuscula. a. Germinal 

 corpuscles at the base of the secondary embryo-sac. c. Four cellular fila- 

 ments or suspensors, which are developed from the germinal corimscles 

 after impregnation, d. One of these suspensors, with the embryo (em) 

 at its apex. 



E. Brown, their discoverer, are very much like the arcJiegonia 

 in the internal prothallium-structure of Selag in ella " {Ljco-po- 

 diacepe, p. 769, and/_^. 1113). 



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

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

 micropyle, and send 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 



