IO4 Elementary Biology. 



the leaf is broad at its base and pointed at its free end. It is 

 sessile, i.e. has no stalk, and is attached directly to the stem. 

 In those species which possess an axial bundle of elongated 

 cells, the leaf shows a central nerve, or midrib, of similar 

 cells, continuous with those of the axial strand. The margin 

 of the leaf commonly bears minute spines. The leaves are 

 arranged in a definite order round the stem, approaching 

 to a more cr less perfect spiral. 



It has been already remarked that the thallus had the 

 power of throwing out from itself a stolon or shoot, which, 

 after creeping along the ground for some distance, could 

 take root, and develop into an independent plant. This 

 method of multiplication is a form of vegetative repro- 

 duction, and it is a method especially common amongst 

 mosses, and is by no means confined to the production of 

 stolons. The first stage in the formation of a new plant, 

 by vegetative multiplication from the root, is the production 

 of a small branched green intermediate thallus known as a 

 protonema, from which springs the erect stem of the thallus 

 proper. 



Reproductive organs. The essential organs of repro- 

 duction are borne at the free termination of the stem 

 surrounded by an involucre of leaves. The male organs 

 may be borne on the same stem as the female organs, or on 

 different plants. If on the same thallus, the spermaria and 

 ovaria may be intermingled or may be arranged so that the 

 ovaria are central whilst the spermaria surround them. The 

 involucres differ slightly in the character of their leaves 

 according to the sex. In Polytrichum the sexual organs are 

 borne on different stems on distinct plants. 



The spermarium is an elongated sac, the wall of which 

 is composed of many cells arranged in a single layer deep. 

 The cells contain chlorophyll bodies imbedded in the gran- 

 ular protoplasm. The sac is filled with cellular tissue, the 

 mother cells of the sperms. The contents of each cell 

 become gradually transformed into a sperm, round which, 



