214 



MOSSES AND FERNS chap. 



branches. The section of the former is triangular, and its epi- 

 dermis provided with hairs which are absent from the epidermis 

 of the aerial parts. Rudimentary scales, arranged in three rows, 

 are present, and corresponding to these are strands of tissue 

 that represent the leaf-traces of the aerial stems. The central 

 cylinder is much larger relatively than in the leafy branches, 

 and its cross-section is not continuous, but is interrupted by 

 three " pericyclic sectors," composed of cells whose walls are 

 but little thickened. The point of each sector is at the peri- 

 phery of the medulla, or central cylinder, and the broad end 

 toward the centre. As might be expected, intermediate con- 

 ditions are found where the rhizome begins to grow upward to 

 form a leafy branch. 



The male inflorescence of the Polytrichaceae is especially 

 conspicuous, as the leaves immediately surrounding the anther- 

 idia are different both in form and colour from those of the 

 stem. They are broad and membranaceous, and more or less 

 distinctly reddish in colour. A well-known peculiarity of these 

 forms is the fact that the growth of the stem is not stopped 

 by the formation of antheridia, but after the latter have all 

 been formed the axis resumes its growth and assumes the 

 character of an ordinary leafy branch. This, of course, indicates 

 that, unlike most of the Mosses, the apical cell does not become 

 transformed into an antheridium, and the researches of Hof- 

 meister,^ Leitgeb,''^ and Goebel ^ have shown that this is the 

 case. The antheridia form groups at the base of each leaf of 

 the inflorescence, and Leitgeb thinks it probable that each 

 group represents a branch, i.e. the inflorescence is a compound 

 structure, and not directly comparable to the simple male 

 inflorescence of Funaria. The sporogonium in Polytrichum 

 has a large intercellular space between the inner spore-sac and 

 columella as well as the one outside the outer spore-sac. In 

 both cases the space is traversed by the conferva -like green 

 filaments found in the other stegocarpous Mosses. The apo- 

 physis is well developed, especially in Polytrichum, and the 

 calyptra very large and covered with a dense growth of hairs 

 (Fig. 1 06, D). 



The structure of the peristome in the Polytrichaceae is 

 entirely different from that of the other Mosses. It is com- 

 posed of bundles of thickened fibrous cells arranged in crescent 



1 Hofmeister (2). ^ Leitgeb (9). ^ Goebel (7). 



