268 RELATION OF PLANT PROTOPLASM TO ENVIRONMENT. 



Over the hot desertic expanses of the Chihuahuan area in N. America, the 

 Sahara and the Karroo of Africa, or the interior plains of Australia, groups of 

 plants belonging to quite distinct families grow, and sometimes even attain to 

 great stature, under temperature and light conditions that might seem impossible. 

 Thus the yucca, the agave, the cactoid and the xerophitic leguminous groups of 

 the Chihuahuan areas; the grape-vines, the geranioids, the stapelias and the 

 aloes of Africa ; the proteads, eucalyptoids, the verticordias and other Myrtacese, 

 also the Leguminosse of Australia are exposed in their leaves or in their shortened 

 stems to an intensity of temperature that must often register 60° to 65° C, and 

 which must be fully felt in the epidermal cells at least of the more succulent types, 

 and throughout the tissues generally in the many dry leathery ones of these 



regions. 



The behavior of the Californian plant Lewisia rediviva alone is instructive. 



In the Botanical Magazine it is said that the specimen there figured from Kew 

 was "one of many which, when gathered with a view of being preserved for the 

 herbarium, in British Columbia, by Dr. Lyall, R. N., of the Boundary Expedition, 

 was immersed in boiling water, on account of its well-known tenacity of life. 

 More than one and a half years after, it, notwithstanding, showed symptoms of 

 vitality, and produced its flowers in great perfection in May of the present year, 

 in the Royal Gardens of Kew." 



Kerner (22a) and Schimper (29) have both cited cases where, over extensive 

 areas the heat, the cold, and the light influence must all be pronounced. The 

 former cites Chinchoxo on the Loango coast where the soil layer may be 75 

 85° C, and Yakutsk in Siberia where - 62° and - 63.2° C. (the lowest temperature 

 hitherto generally observed on the earth) were noticed. There for months the 

 temperature in the shade does not rise above — 30°, but numerous herbs and shrubs 

 are found whose upper organs are exposed for weeks to a degree of cold at which 

 mercury freezes." 



But it must equally be emphasized that many plant species have a definite 

 physiological minimum and maximum, during the vegetative period, that may 

 lie between comparatively narrow limits of temperature. Thus the writer (30) 

 has shown not only that related species of Crocosma may live or die as they are 

 exposed to slightly different degrees of cold, but that the hybrid between these 

 may show a fairly exact mean between the two. He has also stated that a like 

 condition holds for Philesia, Lapageria and their hybrid. Even the units of heat 

 needed to bring hybrids into bloom seem to be — from the writer's studies that 

 have been extended by others since — fairly intermediate in amount between 

 those needed for the parents, if these bloom at different dates. 



In summary it might be said that if plant protoplasm shows an adaptability 

 even in spore cells and seeds from 85° C. to 100° C. over long periods, and also to 

 temperatures from - 100° to - 250° C, those cases where it shows a less degree 

 of adaptability probably represent an acquired condition, in which, owing 

 absorption of extra water by the protoplasm, it is thereby rendered more un- 



