422 



BOTANY 



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 (proteid substances in 

 Marchantia, cane-sugar in the case of Mosses ( 96 )) an attractive 

 stimulus on the spermatozoids. The spermatozoids, thus directed 

 toward the neck of the archegonium, traverse it as far as the egg, 



into which one sper- 

 matozoid penetrates. 

 The water necessary for 

 the process of fertilisa- 

 tion is supplied by rain 

 or dew. After fertilisa- 

 tion has been accom- 

 plished, the egg - cell 

 divides and gives rise 

 directly to an embryo 

 ((7), without first, as is 

 usually the case in 

 oospores, undergoing a 

 period of rest. 



The Mosses as well 

 as the Pteridophytes 

 multiply also asexually 

 by means of SPORES 

 provided with cell-walls 

 and adapted for dis - 

 semination through the 

 air. These two modes 

 of reproduction, sexual 

 and asexual, occur in 



io.&76.-Mar<'Jtan1iai*>l!iniori.li<t. A, Young, JB, mature arch,-, regular alternation, and 



gonium ; C, fertilised archegonium, with dividing egg-cell ; are Confined tO sharply 



f, neck-canal-cell ; A"', ventral-canal-cell ; o, egg-cell ; pr, di st i nct generations : a 

 pseudo-perianth, (x 540.) . 



sexual (gametophyte), 



provided with sexual organs, and an asexual (sporophyte), which 

 produces spores. The sexual generation arises from the spore ; 

 the asexual from the fertilised egg. The number of chromo- 

 somes in the nuclei of the sporophyte is twice as. great as in the 

 nuclei of the gametophyte. The double number is acquired in the 

 fusion of the sexual nuclei, while the reduction to one half takes 

 place in the division of the spore-mother-cells. THIS ALTERNATION 

 OF GENERATIONS is characteristic of all Archegoniatae. 



In the development of the SEXUAL GENERATION, the unicellular 

 spore on germinating ruptures its outer coat or EXINE, and gives rise 

 to a germ-tube. In the case of the Hepaticae, the formation of the 



