364 PART III. THE CLASSIFICATION OF PLANTS. 



cortex. The stem-leaves have, at the base, a pair of lateral appendages, the 

 auriculae. 



The leaf consists of a single layer of cells, and has no midrib. It is made up 

 of two kinds of cells : large empty cells of various forms with perforated walls 

 frequently with spiral or some similar form of thickening : small cells, arranged 

 between the proceeding, containing protoplasm and chloroplastids. The relative 

 arrangement of these two kinds of cells affords a means of classification. Nostoc 

 and other Algae are frequently found in the large empty cells. 



The Sphagnaceae have no special organs for vegetative propagation ; but they 

 multiply vegetatively by the dying away of the main stems so that the lateral 

 branches became separate and constitute distinct plants : consequently these 

 plants are found in considerable masses. They inhabit damp, boggy spots, and 

 retain a considerable quantity of water in the open cells of the branches and 



JOS 



Fis. 218. Longitudinal section (diagram- 

 matic: x 19) of the sporogonium of Sphag- 

 num: ps pseudopodium ; /foot; c calyptra 

 FIG. 247. Part of shoot of Sphagnum with neck of archegonium 7i; a arche- 



acutifolium (nat. size). Ic Capsules. sporium. 



leaves. Masses of Sphagnum thus saturated with water form peat-mosses or 

 peat-bogs, the water being raised to the surface by means of the capillary 

 system formed by the open cello. 



B. The SPOKOPHYTK. The oospore, as in other Mosses, is divided by the 

 transverse basal wall into an epibasal and a hypobasal half. The epibasal half 

 gives rise to the capsule : it grows at first apically, segments being formed by trans- 

 verse walls, each segment being divided into four cells (quadrants) by walls at 

 right angles to each other: after six or eight segments have been formed, apical 

 growth ceases, the further growth being intercalary. The cells of each segment 

 become differentiated each into an external and an internal cell ; the external 

 cells constitute the amphithecium, the internal cells the endothecium. The 

 ainphithecium comes to consist of several layers by periclinal divisions, the 

 first formed and most internal layer constituting, in its upper half, the arches- 

 porium ; the endothecium constitutes the columella. Thus the archesporiuin is 

 a hollow hemisphere which covers the columella as a cap. There is no intercel- 

 lular cavity formed in the capsule. 



