GROUP II. BUYOPHYTA: MUSCT. 357 



is either leafless or bears a few leaves like those of the sterile 

 shoot. 



In Sphagnum and Andreeea, the apex of the female shoot grows 

 oat, after fertilisation of the archegonium, into a long leafless 

 shoot termed a pseudopodium, which bears the sporogonium (here 

 destitute of a seta) at its apex. In Aulacomnium and Tetraphis 

 there is a somewhat similar terminal shoot, likewise termed a 

 pseudopodium, which bears at its apex a cluster of gemmae. 



The Leaves present considerable variety in size and form (hetero- 

 phylly, see p. 57) : they may be divided, in the first instance, into 

 foliage-leaves and involucral leaves. 



The foliage-leaves are simple and sessile; they are usually 

 inserted transversely on the stem, and are closely packed. They 

 are generally larger towards the upper than towards the lower 

 part of the shoot. In most pleurocarpous Mosses the leaves of the 

 lateral branches differ more or less from those of the main stem. 

 In some forms (e.g. Bryum roseum, Cliinacium, etc.), where the 

 branches take the form of creeping runners or stolons, the leaves 

 of these branches are reduced to scales (cataphyllary leaves). 



The involucral leaves are arranged in one or more whorls, 

 forming an involucre round the sexual organs. Those surrounding 

 a group of male organs are commonly larger than the foliage- 

 leaves, and in some cases (e.g. Polytrichaceae) are coloured red or 

 yellow. Those surrounding a group of female organs differ but 

 little from the foliage-leaves : the more internal leaves are smaller 

 than the external : the innermost leaves, distinguished as perichce- 

 tial leaves, are quite rudimentary when the archegonia are mature, 

 but after fertilisation has taken place they grow up round the base 

 of the seta of the sporogonium. 



The Sexual Organs are borne in groups (rarely singly) at the apex 

 either of the main shoots (acrocarpous}, or of lateral branches 

 (pleurocarpous), surrounded by involucral leaves, each group with 

 its involucre constituting a receptacle. Generally speaking the 

 growth of the shoot or branch ceases with the development of the 

 sexual organs, the apical cell itself giving rise to an antheridium 

 or an archegonium ; but in some male receptacles (e.g. Poly trichacese 

 and some other Bryineae, also Sphagnum) the apical cell persists as 

 such ; consequently the elongation of the shoot or branch is not 

 necessarily arrested by the development of the antheridia, and 

 appears to grow through the receptacle. 



Among the sexual organs there are usually present multicellular 



