4 MOSSES AND FERNS chap. 



the young sporophyte of the Pteridophyte, Hke that of the 

 Bryophyte, Hves for a time parasitically upon the gametophyte. 

 Sooner or later, however, the sporophyte becomes entirely 

 independent. This is effected by the further growth of the 

 primary root, which brings the young sporophyte into direct 

 communication with the earth. The primary leaf, or 

 cotyledon, enlarges and becomes functional, and new ones 

 arise from the stem apex. Usually by the time this stage 

 is reached the gametophyte dies and all trace of it soon 

 disappears. In some of the lower forms, however, the game- 

 tophyte is large and may live for many months, or even years, 

 when not fecundated, and even when the sporophyte is formed, 

 the prothallium (gametophyte) does not always die immediately, 

 but may remain alive for several months. The spore-forming 

 nature of the sporophyte does not manifest itself for a long time, 

 sometimes many years, so that spore-formation is much more 

 subordinate than in the highest Bryophytes. With few excep- 

 tions the spores are developed from' the leaves and in special 

 organs, sporangia. In the simplest cases, i.e. Ophioglossum, 

 the sporangia are little more than cavities in the tissue of the 

 sporiferous leaf, and project but little above its surface. 

 Usually, however, the sporangia are quite free from the leaf 

 and attached only by a stalk. These sporangia are in the 

 more specialised forms of very peculiar and characteristic 

 structure, and are of great importance in classification. 



Corresponding to the large size and development of special 

 organs in the sporophyte of the Pteridophytes, there is a 

 great advance in the specialisation of the tissues. All of the 

 forms of tissue found in the Spermaphytes occur also among the 

 Pteridophytes, which indeed, so far as the character of the 

 tissues of the sporophyte is concerned, come much nearer to the 

 former than they do to the Bryophytes. This is especially 

 true of the vascular bundles, which in their complete form 

 are met with first in the sporophyte of the Pteridophyta. In 

 size, too, the sporophyte far exceeds that of the highest Mosses ; 

 while in these the sporogonium never exceeds a few centimetres 

 in extreme height, in some Ferns it assumes tree-like pro- 

 portions with a massive trunk lo to 15 metres in height, 

 with leaved 5 to 6 metres in length. 



In the formation of the spores all of the Archegoniata; 

 show great uniformity, and this extends, at least as regards 



