362 BOTANY. 



face of the prothallium, and consist of masses of cells, enclos- 

 ing in each case a single cell, which develops into one germ- 

 cell (in the archegonia), or a number of sperm-cells (in the 

 antheridia). The sperm-cells produce spirally coiled sperma- 

 tozoids, which fertilize the germ-cell by passing down the 

 canal in the neck of each archegonium. In many of the 

 plants of this division there is a strong tendency toward 

 dioeciousness in the prothallia, and in the higher genera it 

 becomes the invariable rule. 



470. The result of fertilization is the formation of a 

 young plant, by the growth and successive division of the 

 fertilized cell. In its first stages the new plant is usually 

 quite simple, but it soon becomes, in the greater part of the 

 Division, a leafy plant with highly developed tissues. After 

 a greater or less period of vegetation the new plant produces 

 spores by the internal cell-division of certain mother-cells, 

 each of the latter producing four spores. The particular 

 structure of the spore-bearing organs and the place of their 

 appearance are quite different in the different classes. In 

 many cases they are produced upon the surface of the 

 ordinary green leaves, in other cases upon modified leaves, 

 while in still others upon the bases of the leaves, in their 

 axils. The spores are in most cases of one kind, but in 

 certain genera there are large spores (macrospores), and small 

 ones (microspores). 



471. True roots first make their appearance in this 

 division. A root is developed upon the young plant, but 

 this never attains a great size, and others form in acropetal 

 order upon the Mem, and even occasionally upon the leaves. 



472. In the Pteridophytes the three tissue systems epi- 

 dermal, fibro-vascular, and fundamental attain a good de- 

 gree of development. The epidermis is distinct, and con- 

 tains stomata similar in form and position to those of the 

 Phanerogams. In many cases there is a strong development 

 of trichomes, as in the Ferns, where the young leaves are 

 usually densely covered with scurfy hairs. The fibro-vascu- 

 lar bundles are always closed, and generally are what De 

 Bary calls concentric bundles ; in the Equisetinse, however, 

 collateral bundles occur, and in Lycopodinae radial bundles. 



