260 



Scientific Proceedings, Royal Dublin Society. 



Fusion Sorus. — Both the sorus and the commissure are situated midway 

 between the margin and the midrib. It is a mixed sorus, and in the mature 

 condition, at any rate, is devoid of an indusium. It becomes a question of 



Fig. 3. — T. blec/moides. 

 Qi) Venation of sterile leaf, (b) Venation of fertile leaf, showing commissural vein. 



interest whether or not an indusium is present in earlier stages of develop- 

 ment. The youngest material available is that figured in Fig. 4, from 

 which it is seen that the indusium at that stage is absent. From this 



-f-rv^n r~nc > 



Fig. 4. — T. blechnoides. Transverse section through sorus. 



drawing may also be seen the mixed character of the sorus ; some of the 

 sporangia being mature and their spores shed, while others are in the initial 

 stages of development. A vein, which is the commissural vein, directly 

 underlies the sorus. This commissure and its relation to the sorus is seen 



