THE PTERIDOPHYTA : FILICALES, THE FERNS 505 



second year a minute lamina forms, folded over the apex of the petiole, but 

 it is not till the third season that the petiole comes above ground and the 

 lamina expands to its full size. Both stem, apex and young leaf are thickly 

 set with brown ramenta, but the leaf sheds them as it grows. 





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Fig. 496. — Pteridiiwi aqidlinum. Longi- 

 tudinal section through the apex of 

 the rhizome showing the apical cell 

 and differentiation of meristeles. 

 {After Chang.) 



At the bases of the first two leaf pinnae there are nectaries, little sunken 

 patches of tissue from which a sugary secretion escapes, through the stomata. 

 Their function is unknown. 



FIRST 

 LEAVES 



SOIL LEVEL 



LEAF 



Fig. 497. — Pteridium aquilinnm. Primary dichotomy of the rhizome. 



{After Boiver.) 



17A 



