428 



BOTANY 



PART II 



into the egg-cell (Fig. 368, J, o) and the ventral -canal -cell {k"). 

 The latter is situated at the base of the neck, just below a central 

 row of neck -canal -cells (//). On the maturity of the archegonium, 

 the ventral- and neck-canal-cells become mucilaginous and dis- 

 organised. 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 {^'-^)) 

 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 spermatozoid penetrates. The water necessary 

 for the process of fertilisation is 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 

 oospores, undergoing a period of rest, 



Antheridia and arcliegonia aru developed by cell-divisiou from .single supeifieial 

 cells of the thalliis, and are homologous organs ; their homology is supported by 

 the occurrence of structures intermediate in nature. The ventral-canal-cell and 

 the canal-cells thus correspond to gametes which have become functionless. 



The behaviour of the sexual nuclei requires further investigation. According 

 to the observations of W. and C. van Leeuwen-Reijnvaan on Folytrichum and 

 Mnium it appears that in the last division of each spermatogenous cell to give rise 

 to two spermatozoids the nucleus is halved in such a way that each daughter- 

 nucleus shows only half the haploid number of chromosomes ; this is not a 

 reduction division. The mother-cell of the ovum of Folytrichum appears to behave 

 in the same way. The two daughter-cells by again fusing form the egg-cell, and 

 this is then fertilised by two spermatozoids of the half-value (^''"). 



By the division of the fertilised egg (Fig. 367, C) a multicellular 

 embryo is formed, which, by its further development, gives rise to 

 the second or asexual genehation, represented by the sporogonium 

 or the stalked MOSS CAPSULE. The sporogonium, in most cases, 

 consists of a round or oval capsular receptacle, in whose internal 

 tissue numerous unicellular spores are produced. In both the 

 Bryophytes and Pteridophytes the spores are formed in tetrads by 

 the twice-repeated division of the spore-mother-cells, which previously 

 have separated from one another and become rounded off. The spore 

 capsule has usually a shorter or longer stalk, of which the basal 

 portion, or foot, remains in the distended venter of the archegonium, 

 and, in consequence of the overgrowth of the underlying tissue, has 

 the appearance of being sunk in it. Although the sporogonium 

 constitutes a distinct asexual generation, it continues throughout its 

 existence united with the sexual generation, and, like a semi-parasitic 

 plant, draws from it the nourishment necessary for its development. 



There are ilifliculties in tlic way of tlic pliylogenetic derivation of the Bryoi)hyta 

 from any definite group of Algae. Between the Bryophytes on tlic one luuul, and 

 the liighcr Green Algae and Cliaraceae on the otlier, no transitional forms are 



