IX MARATTIACE^—ISOETACE^ 293 



complete. From this time on, the reL^ular succession of 

 sporophylls 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 Bruchman ' and Kienitz- 

 Gerloff," but Farmer " 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 

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

 like that of OpJiioglossuni vulgatiun, 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 corresponding 

 to each furrow.* According to Bruchman '' 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 calyp- 

 trogen and dermatogen. The periblem 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 Bruchman. He states that 

 the process begms 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. 



TJie SporangiujH 



The development of the sporangium has been very carefully 

 examined by Goebel,'' and his results confirmed by later 

 observers. All of the leaves, except the imperfect ones that 

 separate the sporophylls of successive years, bear a single, very 

 large sporangium at the base. From the first it consists of an 



' Bruchman ( I ), p. 554. - Kienitz-Gerloff (6). 



•' Farmer (2), p. 37. "* \'an Tieghem and Douliot (5). 



' Bruchman (i), p. 558. « Goebel (3), Bot. Zeit. 1881. 



