343 BOTANY. 



437. — Fertilization takes place by the spermatozoids find- 

 ing their way down the neck of the archegoninm (open at 

 this time) and uniting their substance with that of the germ- 

 cell. The first result of fertilization is the formation of a 

 wall upon the germ-cell, which then begins to divide into 

 a mass of cells by the formation of diagonal partitions. 



438. — The sexual organs are generally numerous, and 

 they are frequently produced in little clusters of several to- 

 gether, surrounded by enveloping leaves (the perichcBtium) , 

 thus forming a sort of flower. In some species the anther- 

 idia and archegonia are in the same flowers QiermajJlirodite), 

 while in others they are upon different parts of the same plant 

 {tnonmcious), or upon entirely different plants (dmcious). 



439. — The second, or asexual, generation is always devel- 

 oped from the fertilized germ-cell belonging to the first ; but 

 while it is nourished by the latter, there is no organic con- 

 nection between the sexual and the asexual generations. 

 The asexual generation consists of a spore-case, or s^joro^o- 

 ni 11,111, with a greater or less developed stalk, or aeta, support- 

 ing the former. The spore-case varies much in form and 

 -degi'ee of complexity, l)oing in some cases but a globular 

 body filled with spores, while in others its structure is quite 

 complex, and difficult to understand. 



440. — The spores are produced from mother-cells, each of 

 "which gives rise by internal cell-division to four daughter- 

 cells, the spores. The mature spores are provided with a 

 double wall, the outer (exospore) being usually hard and 

 somewhat roughened, while the inner {enclospore) is thin and 

 ■elastic. The interior of the spore is composed of colorless 

 protoplasm, chlorophyll granules, starch, and minute drops 

 of oil. In germination the endospore breaks through the 

 exospore, and becomes prolonged as a narrow tube, which by 

 division gives rise to the sexual stage of the plant. 



44'1. — In a portion of the Division the plant-body is either 

 a true thallus, or a structure which is best described as 

 thalloid in form ; in all of the Mosses, however, and some of 

 the Liverworts, there is a differentiation into stem and leaf. 



442. — No true roots are found in the Bryophyta, but in 

 T;)lace of them there are root-hairs, consisting of single cells. 



