4 MOSSES AND FERNS chap. 



primary root, which brings the young sporophyte into direct 

 communication with the earth. The primary leaf, or cotyle- 

 don, 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 gametophyte 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 

 exceptions the spores are developed from the leaves and in 

 special organs, sporangia. In the simplest case, e. g., Ophio- 

 glossum, 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; 

 w^hile in these the sporogonium seldom exceeds a few centime- 

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

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

 leaves 5 to 6 metres in length. 



In the formation of the spores all of the Archegoniatse 

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

 the pollen spores, to the Spermatophytes as well. In all cases 

 the spores arise from cells which at first form a solid tissue 

 arising from the division of a single primary cell, or group of 

 cells (Archesporium). These cells later become more or less 



