NYLANDER ON THE ALGO-LIOHBH HYPOTHESIS, &0. 1 19 



ledge of these, oven in their proportions (an equal part) ? I should 

 certainly Buppose that anyone teaching that lichens draw their 

 Donrishmenl from the atmosphere, by no means understands by the 

 term " atmosphere " only dry air, but chiefly rain-water with all 

 the different Bubstances which it may contain ami bring with it. Or 

 who has affirmed, who ever would affirm, that lichens can derive 

 all the parts constituting their organisation from pure air ^oxygen, 

 azote, carbonic acid)? And who, also, would affirm that rain- 

 water is the same as the distilled water of the chemist's laboratory ? 

 But we may correctly say that pure or naked air (if the expression 

 may be allowed) is by no means adapted for the food of lichens, 

 but by drying them up checks and represses their nourishment ; 

 though at the same time they do not love places which are not open 

 to salubrious air. It is manifest that the air does not directly 

 nourish them. So far, however, as relates to the manner in which 

 lichens draw their nourishment (aerial, solid, and in solution) from 

 water or by means of water (atmospheric or other), it can very 

 easily be shown that it chiefly penetrates through the surface of the 

 thallus (the cortical stratum). And how far the nature of the sub- 

 stratum is indifferent to them is evident from the circumstance that 

 very many of them occur promiscuously on the most diverse sub- 

 strata. Thus the same lichens occur on the hardest rocks, on dry 

 wood (even indurated by dryness), or on dead bark ; from all of 

 which they assuredly could not extract similar aliment, if, indeed, 

 they were able to annex even any particles to themselves. What, 

 for example, is to be derived from the old sapless bark of a pine ? 

 or what analogous from a quartzose rock ? But the same Lichens 

 grow alike on both. Nor is it to be overlooked that many of the 

 same are at the same time muscicole, and often only loosely affixed — 

 which very dissimilar stations, nevertheless, would seem to present 

 similar food, for these plants remain most similar in all ; nor is the 

 substratum lying under them (under the thallus, hypothallus, or 

 gomphus) ever observed to be worn or comminuted. From all 

 these reasons, then, we may conclude that the substratum is 

 scarcely of any importance, so far as nutrition is concerned. But, 

 in addition to this, lichens are so formed that foreign elements 

 usually could not, or could only with difficulty, arise from the sub- 

 stratum. The crustaccous thalli, indeed, not rarely exhibit under 

 the cortical gonidial stratum a tartareous medulla, or thick deposit, 

 not readily permeable, and nearly dead, and often a hypothallus 

 conglutinating the lichen closely to the stone, and this also but 

 little pervious.* But by a very simple and easy experiment the 



* Here the author adds, in a note in my copy — " The same is observed in terres- 

 trial or museieole fruticulose thalli, fortbeir lower part next to the substratum is 

 destroyed and seen to be dead, when the upper parts only of the lichen are iu 

 full vigour. The life thus being lost in the part contiguous to the substratum, 

 nothing through it can arise from the Bubstratum. The nutritious elements, 

 indeed, in these lichens, as iu the others, are received through the external and 

 upper parts." 



