342 BOTANY. 



437. Fertilization takes place by the spermatozoids find- 

 ing their way down the neck of the archegonium (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 perickcstium), 

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

 idia and archegonia are in the same flowers (hermaphrodite), 

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

 (monoecious), or upon entirely different plants (dioecious). 



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 sporogu- 

 nium, with a greater or less developed stalk, or seta, support- 

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

 degree of complexity, being 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 (endospore) 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. 



441 . 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 

 place of them there are root-hairs, consisting of single cells. 



