PI 



a 



Fig. 217-— Longitudinal section oi Macrocystis ^yrifera. showing 

 sieve-tubes, /, and sieve-plates, j, with callus (x 3C0). (After 

 Oliver.) 



Fig. 216. — Chorda filuin Stackh. «, uppermost and lowermost ;)ortion of frond (natural size); b, 

 transverse section, she win aj differentiation into cortical and epidermal layers (x 200). (After Hauck.) 



R 2 



