RELATION OF PLANT PROTOPLASM TO ENVIRONMENT. 265 



Pasteur found that the dry conidiospores of Penicillium ghucum could endure 

 a temperature of 108° C, but that in liquid they were killed at 100° C. The dry 

 spores of species of Smut (Ustilago) survive heating to 104°-120° C, but when 

 moist are killed at a temperature of 60°-73° C. Chodat (20) exposed spores of 

 Mucor mucedo to a temperature of— 70° to — 110° C, and even considered that 

 the mycelium may be equally frozen. He concludes that "la vie est conditionnee 

 par certaines structures. Les forces qui les mettent en jeu peuvent etre des 

 forces toutes physiques. Elles sont simplement les sources d'energie qui pourront 

 mettre la machine en mouvement." 



But the behavior of many lichens in the vegetative state is highly instructive, 

 compounded as they are of a fungoid and of a schizophyceous algal constituent. 

 Growing on bare open rocks, they may be exposed for a few hours or days to rain, 

 and then for weeks or months mayhap to broiling suns. Along the French 

 Riviera coast in July the writer has placed his hand alongside some of these as 

 they grew on the red rock, and had speedily to withdraw it again as a matter of 

 comfort. Kerner (22) says regarding them: "The crustaceous lichens adhering 

 to the limestone rocks of the wild regions of the Karst of Istria and Dalniatia 

 {Aspicilia calcarea, Verrucaria purpurascens , and V. calciseda) are regularly 

 exposed on cloudless summer days to a temperature of 58° to 60° without injury, 

 and the edible lichen (Lecanora esculenta), is often heated in the deserts, along 

 with the stone on which it grows, to fully 70°, and yet is not destroyed/' 



Few exact records have been published for the mosses, and a promising field 

 for inquiry is here open. But the recent studies of Irmischer (31) suggest future 

 extended observations that will yield important results. 



While ferns are as a group umbrophilic plants, it can equally truly be said 

 that species of Pellcea — e. g., P. atropurpurea — Notholcena, and some epiphytic 

 tropical species of Polypodium are truly thermophilic. The leaves of such 

 species are often smooth and leathery ; they contain a relatively small amount of 

 moisture even after rain; they grow on exposed gray-white rock faces, or epi- 

 phytically on dry tree trunks; they may remain shrivelled and apparently dead 

 for weeks or even months without moisture other than dew; at times even hot 

 dry winds accentuate the often intense insolation. Yet they live unharmed at 

 temperatures which may run from 65°-70° C. 



On the hot white sandy knolls over the savannahs near Wilmington, N. C, 

 Selaginella acanthonota has its hard wiry patches of branches exposed for weeks to 

 direct day temperatures of 60°-65° C, while its near ally the well-known resur- 

 rection plant of California and Mexico (Selaginella lepidophylla) can not only 

 endure such heats, but will live for months out of the ground in a box, and if 

 again planted will unfold its shoots, revive and grow. 



In all of the above sun-exposed plants, it is evident that — no matter what 

 view we may hold as to the function of cuticle and epidermis in relation to 

 subjacent cells— the epidermal cells at least were exposed to all of the constituent 

 rays of an intense light. 





