BOTANICAL SUBJECTS. 



219 



the two kinds of cells are mixed up in the frond ; but in lower 

 unicellular plants there is no such thing as separate vegetative 

 cells. 



In the double indusium of Pteris Aquilina we have a suggestion 

 which is worth noting. I shall lead up to what it strongly 

 suggests presently. 



First in TVoodsia hyperhorea, Br., we have the separate sori 

 on the nodes of the veins, each sorus being surrounded by an 

 involucre of hairs (Fig. 73). An almost parallel of this in 



Fig. 73. Sorus of Woodsia hi/jjerborea Tig. 74. Arillate ovule of Myristica 

 (Hook., " Br. Bot.,*' pi. 7). (Le Maout and Decaisne, p. 651). 



phoenogams is to be found in the arillate ovule of Myristica, 

 Fig. 74. 



Then in Woodsia Ilvensis, Br., we have these same separate 

 sori — each still surrounded by an involucre of hairs — arranged in 

 rows along the margin of the pinna, with the margin slightly 

 turned over them. 



Finally, in Fteris Aquilina (Fig. 75) we have the sori 

 confluent all along the margin of the pinna, with the involucral 



Fig. 75 . Portion of marginal placenta oVPteris Aquilina 

 (Hook., " Br. Bot.," pi. 38), (a a) confluence of sori. 



