68 JOURNAL OF THE [J uly, 



Stipe, the algae are carried through to the outer surface and follow 

 in luxuriant growth its upward course. Only a comparatively 

 few scattering clusters occur in the discocarp and cavities and 

 tissue of the stipe. On the periphery of the receptaculum, how- 

 ever, there is an unusual growth of algae, loosely bound together, 

 and sparingly covered by the filaments. Not a little attention 

 was given to this peculiar development. The ease with which 

 they could be separated, and the simplicity of their growth, readily 

 suggested that they might be means of propagation, though the 

 significance of their position on the stipe rather than on the thal- 

 lus was not manifest. I can see only one explanation of this 

 distribution of the gonidia — namely, that the algae are massed 

 along the stipe, exposed directly to the atmosphere, unrestrained 

 in their growth by the pressure of a medulla, in order that they 

 may be able to meet with an adequate food supply the heavy 

 demands made upon their constructive metabolism by the asco- 

 genous hyphse. This appears to be an excellent illustration in 

 vegetable physiology of adaptation to economic ends. And this 

 seems the more probable as the rhizoids are the last stage in the 

 reduction of root forms. Although the algee are in a limited de- 

 gree histological factors of the thallus, being dependent upon the 

 fungi, it may be, for their ash constituents, nevertheless it is more 

 in keeping with the nature and behavior of lichens to look upon 

 the fungus simply as an obligate parasite and the alga as a host. 

 And then again it was often observed that on the old sporophores 

 the gonidial bundles began to grow after the manner first de- 

 scribed, and at times quite covered the stipe with small thalli. This 

 secondary growth on the receptaculum was not observed while 

 the asci were still developing. 



The results of the consortism of these two plants is particularly 

 worthy of note. On the one hand, the fungus, delicate, a sapro- 

 phyte, fond of darkness and dampness, and the alga, dependent 

 upon shade and moisture, by their commensalism produce a plant 

 independent of surroundings and organic substratum, capable of 

 living upon crystalline rock or bark of tree or earth, enduring the 

 extremes of heat and cold, neither dependent upon rain nor de- 

 stroyed by drought. And this complete change of habit is not so 

 striking as the behavior of these two lowly plants as symbionts. 

 They at once catch the spirit that governs all higher vegetable 



