382 



BOTANY 



and enclosing numerous small cells, each one of which is the mother- 

 cell of a spermatozoid (Fig. 310). At maturity the spermatozoid 

 mother-cells separate and are ejected from the antheridium, which 

 ruptures at the apex. By the eventual dissolution of the enveloping 

 walls of the mother- cells the spermatozoids are set free as short, 

 slightly twisted filaments, terminating anteriorly in two long cilia. 



Spermatozoids of similar 



(5k 



form are found among 

 the Thallophytes only 

 in the group of the 

 Characeae. The arche- 

 GONIA are flask -shaped 

 bodies with walls formed 

 of but one layer of 

 cells ; they are sessile or 

 shortly stalked, some- 

 times also somewhat 

 sunk in the tissue, and 

 consist of a dilated ven- 

 tral portion and a long, 

 slender neck. The ven- 

 tral portion encloses a 

 large central cell, the 

 contents of which shortly 

 before maturity divide 

 into the egg -cell (Fig. 

 311, A, o) and into an 

 overlying ventral canal- 

 cell (&"). The latter is 

 situated at the base of 

 the neck, just below a 

 central row of neck- 

 canal-cells (M). On the 

 maturity of the arche- 

 gonium, the ventral and neck -canal -cells become mucilaginous and 

 disorganised. If water is present, the cells at the apex of the neck 

 separate (B) and the mucilaginous matter is discharged, and exerts 

 through the diffusion of certain of its constituents in the water (cane- 

 sugar in the case of Mosses) an attractive stimulus on the sperma- 

 tozoids. The spermatozoids, thus directed toward the neck of the 

 archegonium, traverse it as far as the egg, into which one spermatozoid 

 penetrates. The water necessary for the process of fertilisation is 

 sufficiently supplied by rain or dew. After fertilisation has been 

 accomplished, the egg-cell divides and gives rise directly to an embryo 

 (c), without first, as is usually the case in the oogamous Thallophyta, 

 undergoing a period of rest. 



Fig. 311. — Marchantia polymorplia. A, Young, B, mature arche- 

 gonium ; C, fertilised archegonium, with dividing egg-cell ; 

 k\ neck-canal-cell ; fc", ventral canal-cell ; o, egg-cell ; pr, 

 pseudo-perianth, (x 540.) 



