256 



The Plant World. 



cation of local lichen floras, such as have been prepared for many 

 parts of Europe, taking for a basis a county, a state, or better, 

 some natural biological region. Such floras, with carefully pre- 

 pared keys, will arouse the interest of both amateur and profes- 

 sional botanists and induce them to become acquainted with 

 lichens. The publications of mere lists of species, however 

 valuable to the specialist, is only a bug-a-boo to the beginner or 

 the general botanist. 



In the realm of experimental physiology lichens offer one 

 of the most attractive fields. The spores may be germinated, 

 grown in nutrient cultures, with or without algae, treated with 

 various toxic salts, and their responses to all sorts of stimuli 

 noted. Then there is a vast deal to be learned about their be- 

 haviour under various atmospheric and climatic conditions, 

 their power of growth and continued viability under extremes 

 of heat and cold, their power of retaining moisture during pro- 

 longed drouth, and of absorbing it from various substrata or 

 from humid air. Unfinished experiments by the author show 

 that certain lichens of xerophytic structure maintain a moisture 

 content of 50% during our rainless California summer, while on 

 a rainy spring day some absorb so much water as to increase their 

 dried weight more than 300 per cent. 



Many lichens readily lend themselves to measurements of 

 their annual growth, and while the statements of the texts about 

 the slow growth of lichens are in a measure true, several experi- 

 menters have shown that many lichens are very rapid growers. 

 Such lichens as the Stictas, Peltigeras, Collemas, Lecanora sordida, 

 Lecanora frustulosa, Lecidea fumosa, and many of the Parmelias 

 and Physcias, to name no more, would be admirable for such in- 

 vestigations. To be most valuable, the experiments should 

 extend over several years. 



The influence of ocean water upon lichens would be a good 

 thing for some one living at the sea shore to investigate. A 

 number of lichens, such as Caloplaca coralloides, Catillaria fran- 

 ciscana, and Arthopyrenia halodytes, grow only where they are 

 frequently bathed by the waves, while many others, e. g. Den- 

 drographa minor, grow only where they are constantly moistened 

 by the salt spray. WhatVould be the effect of fresh water on 



