DIV. T 



BRYOPHYTA 



479 



the venter and neck, while the inner cell divides to give rise to the egg -cell, 

 ventral-canal-cell, and neck -canal-cells (Fig. 437). In Mosses, on the other hand, 

 the original cell divides by inclined walls, and the segments of the resulting two- 

 sided apical cell form the stalk. The terminal cell is then divided by three oblique 

 walls and one transverse wall into a three-sided apical cell, truncated below ; a 

 central cell beneath this ; and 

 three peripheral wall-cells. The 

 central cell gives rise to the egg- 

 cell, ventral-canal-cell, and neck- 

 canal-cells ; the segments of the 

 apical cell produce the wall of 

 the neck and the uppermost neck- 

 canal-cells. According to MELIK 

 the Sphagnaceae occupy a middle 

 position in that tlie stalk arises 



FIG. 437. Development of thearchegoniumof a Liverwort. 

 A (longitudinal section) and B (transverse section) 

 showing the upper cell divided by three walls. C, The 

 central cell divided into cap-cell(d) and internal cell (0- 



D, The internal cell divided into the cells which will give 

 rise to the neck-canal-cells Qik), and the ovum and 

 ventral-canal-cells (c) respectively; st, young stalk. 

 (After GOEBEL.) 



as in the Mosses, while the body 

 of the archegonium is differenti- 

 ated without a three-sided apical 

 cell as in the Liverworts. 



Antheridia and archegonia are homologous organs, as is shown by the occurrence 

 of structures intermediate in nature ; the ventral-canal-cell and neck-canal-cells 

 are to be regarded as gametes which have become functionless. The ventral - 

 canal-cell is as a rule smaller than the egg but may equal it in size. Occasionally 

 several egg-cells may be developed in an archegonial venter, e.g. 4 or more in 

 Sphagnum ( 93 ). 



After fertilisation the zygote, without undergoing a period of rest, 

 proceeds to divide and give rise to the embryo (Fig. 436 C). The 



embryo grows into the 



Asporogonium which re- 

 A-X\ . ^^ presents the asexual 



generation and remains 

 throughout its life con- 

 nected with the sexual 

 generation ; it obtains 

 food -materials from the 

 latter like a semi-para- 

 sitic plant. The sporo- 

 gonium is a round or 

 A B oval capsule, with a 



FIG. 438.- A, Summit of the empty antheridium of Polytrichum longer Or shorter Stalk, 

 cut in half and showing the dehiscence cap. (After GOEBEL.) and COntainin " niimer- 

 B, Opened neck of the archegonium of Mnium umlulatum. oug g p Ores These as 



in Pteridophyta and 



Spermatophyta, arise in tetrads by the twice-repeated division of the 

 spore-mother-cells, which have previously separated from one another 

 and become rounded off. 



In the Mosses the lower part of the embryo penetrates into the, often much 

 enlarged, tissue of the stalk of the archegonium and in some cases even into the 



