120 PHILOSOPHICAL NOTES ON 



Simpler than this even we have the unicellular body, which 

 retains throughout its life a spore-like character, and reproduces- 

 itself without becoming a multicellular body. 



The cladophyl of seaweeds then, from which both stem and 

 leaf of phasnogams descended, consisted originally of a simple 

 midrib, which was a condensed cellular chord. From both sides 

 of the midrib less condensed cellular expansions were given off, 

 forming the lamina of the cladophyl. The midrib, where it 

 existed, and the margins of the lamina, where it did not exists 

 were the budding organs. The raison d'etre of the midrib seems 

 to have been originally as a stiffener of the cladophyl, to keep its 

 limp structure from collajDsing. Afterwards, besides a stiffener, 

 it became a carrier of vessels, when the leaf in an atmosj)heric 

 medium had to draw its princijDal nourishment by way of the root. 



"We find an interesting examj)le of the genesis of the stem 

 from the midrib of the cladophyl in Delesseria coriifolia, Fig. 12. 

 This is what Harvey says of this seaweed : — " Frond at first 

 consisting of a linear-oblong or sublanceolate, midribbed leaf, 



Fig. 12. Delesseria coriifolia (" Harvey's Phyc. Austr.," pi. 150). 



which, on the decay of the lamina and thickening oft the rib, is 

 gradually changed into a compressed or imperfectly winged stem. 



