556 MOSSES AND FERNS CHAP. 



Hofmeister states that in I. lacustris the first sporangia are 

 not developed until the fourth year from the time the young 

 sporophyte is first formed. The sporophylls begin to form in 

 the third year, but it is a year more before the sporangia are 

 complete. From this time on, the regular succession of sporo- 

 phylls and sterile leaves continues. 



There has been much disagreement as to the method of 

 growth in the root. The earlier observers attributed to it a 

 single apical cell, not essentially different from that of the true 

 Ferns ; this was shown to be incorrect by Bruchmann ( i ) and 

 Kienitz-Gerloff (6), but Farmer (2) claims that none of these 

 have correctly described the structure of the larger roots, which 

 differs- somewhat from that of the earlier ones. According to 

 the latter observer there is always a single initial for the plerome, 

 and above this two layers of meristem, one giving rise to the 

 inner cortex, the other to the outer cortex, as well as to the epi- 

 dermis and root-cap. The fibrovascular bundle is monarch, 

 like that of Ophioglossum vulgatum, and the phloem becomes 

 differentiated before the xylem elements are evident. 



The later roots arise much as the second one does in the 

 young plant, but the rudiment is more deeply seated. The 

 roots are arranged in /. lacustris in four rows, two correspond- 

 ing to each furrow (Van Tieghem (5)). According to 

 Bruchmann the first evidence of a forming root is a single cell 

 of the cortical tissue lying a short distance outside of the leaf- 

 trace. This, however, cannot be looked upon as the apical cell, 

 as it only gives rise to calyptrogen and dermatogen. The peri- 

 blem and plerome arise from the cells lying immediately 

 below it. 



The branching of the roots is a genuine dichotomy, and has 

 also been carefully studied by Bruchmann (Fig. 321). He 

 states that the process begins by a longitudinal division of the 

 plerome initial, and each of the new initials at once begins to 

 form a separate plerome. The overlying tissues are passive, 

 and their divisions are governed by the growth of the two 

 plerome strands. 



The Sporangium 



The development of the sporangium has been studied by 



Goebel (3), and more recently by Bower (15), and Wilson- 



' Smith (i). Each leaf, except the imperfect ones that sepa- 



