185 



whose cell-nucleus they coalesce. With regard to the formation 

 of the oosphere, it may further be remarked that the lower part of 

 the archegonium originally encloses the so-called " central cell "; 

 but shortly before the archegonium is ripe, this cuts off a small 



portion, the ventral-canal-cell, which 

 lies immediately beneath the neck, 

 and the larger, lower portion be- 

 comes the oosphere. 



The organs mentioned here, antheridia 

 and archegonia, are present in the Crypto- 

 gams (Pteridophyta) and the Gymno- 

 sperms. They have always the same 

 fundamental structure, but with slight 

 modifications of detail. These plants are 

 therefore known as the ARCHEGONIATA. 



The fertilisation of the Mosses 

 cannot be effected without water. 

 Rain and dew therefore play a 

 very important part in this pro- 



Fm. 190. Avdrecea rupestri*. Longi- 

 tudinal section through a sporangium 

 at the time when the mother-cells of 

 the spores are dividing : p pseudo- 

 podium ; / foot ; v vaginula ; 7i neck ; 

 c columella ; w wall of the sporan- 

 gium ; e external row of cells; s the 

 spore-sac ; t the spore-mother-cells ; 

 r the calyptra with the neck of arche- 

 gonium (Zj. 



FIG. 191. Andrecea rupestris. Transverse 

 section through a ripe sporangium. In the 

 middle is seen the four-sided columella, sur- 

 rounded by the numerous spores, drawn dia- 

 grammatically. Surrounding them is seen the 

 wall of the sporangium, whose outer layer *> 

 cells is thickened and coloured. The layer of 

 cells is unthickened in four places (a-) indi- 

 cating the position of the clefts (see Fig. 

 193). 



cess, and for this end various modifications of structure are found. 



