776 LIFE : OUTLINES OF GENERAL BIOLOGY 



times erect, sometimes sprawling, and among terminal clusters of 

 very simple leaves, usually one cell thick, there are developed the sex 

 organs. Both archegonia and untheridia may occur in the same leaf 

 cluster, or they may be in separate clusters. An antheridium is 

 like a simple club; it makes the sperm-mother-cells and liberates 

 them in a little blob, thereafter closing up again. The sperm-mother- 

 cells give rise to spermatozoa with two cilia. When the sexual branch 

 is erect and out of the moisture, it may be difficult for the spermato- 

 zoon to lind any medium in which to swim. This will hinder fertilisa- 

 tion, and many mosses are chiefly multiplied asexually — ^by breakage, 

 by budding, and in other ways. The archegonium is a minute elon- 

 gated flask, with an egg-cell near the base and disintegrating canal 

 cells in the neck, down which a spermatozoon may make its way. 

 From the fertilised egg-cell there develops the sporophyte. Thus the 

 sequence is: 



Spore >■ Protonema -> Fertilised > Dependent > Spore 



with sexual egg-cell sporophyte, 



branches with 



bearing spore capsule 

 sex-organs 



PTERIDOPHYTES. — One of the difficulties in giving even an 

 outline account of the evolution of plants is the gap between the 

 mosses and the ferns, or more technically, between the Bryophytes 

 and the Pteridophytes. Thus D. H. Scott, after a long discussion, 

 remarks that "there is no evidence, fossil or otherwise, for the 

 evolution of the higher Cryptogams from Bryophyta or any plant at 

 all like them. It is more probable that they came direct from plants 

 which were rather of the nature of Algae; this view, however, is a 

 pure hypothesis. . . ." {Evolution of Plants, p. 228.) 



In mosses the sporophyte is leafless and dependent on the gameto- 

 phyte, while in ferns it is a leafy, vascular, well-rooted plant, quite 

 independent of the sexual phase. This is a very striking contrast, 

 which raises difficult problems. 



LYCOPODS OR CLUB MOSSES.— In the great forests of Carbon- 

 iferous times there was an abundant representation of Lycopods, 

 and some of them, called Lepidodendrons, attained the dimensions 

 of huge trees. Their stock can be traced back to the Devonian, when 

 they flourished along with ferns and the like. 



Nowadays there are only four genera of Lycopods : Lycopodium, 

 Phylloglossum, Selaginella, and Isoetes. The common "stag's-hom 

 moss" of the moors is a Lycopodium, but it has no affinity with 

 mosses. In Lycopodium the wiry stem is forked and covered with 

 small leaves; in Selaginella, which is common in greenhouses, 

 the stem is' more delicate, and the life-history, as we shall see, is 



