548 VITAL ACTIONS OF THE LOWER FUNGI. 



to the ashes varies very greatly ; elements are also often 

 absorbed which do not in reality possess the signifi- 

 cance of necessary nutrient materials, and they can pass 

 through the plant or be deposited in various parts of 

 it without exercising any function (for example silicon, 

 aluminium, manganese, &c. ; silicic acid may at times 

 form 50 per cent, of the ashes). It is still uncertain 

 whether anything similar occurs in the case of the 

 fungi ; the analyses which have been as yet made are not 

 sufficiently elaborate to enable us to draw conclusions as 

 regards this point. 



As, according to Na'geli's experiments, potash cannot 

 be replaced by calcium or magnesium, it is probable that 

 the alkalies and the alkaline earths play very different 

 parts ; the latter only appear to form deposits in plasma 

 and in the cell wall, while the alkaline salts are in part 

 dissolved in the free cell fluid. That the potash com- 

 pounds cannot be replaced by sodium or lithium is pro- 

 bably not due to diosmotic differences, but to the less 

 affinity of potash for water ; we may perhaps assume 

 that the salts of sodium and lithium when in a state of 

 solution are surrounded by firmly united molecules of 

 water, which render them unsuitable for contact (Nageli). 



3. Alterations which the Nutrient Materials undergo, 

 and the Functional Activity of the Lower Fungi. 



Relation be- The materials assimilated undergo within the cell a 

 ' series of transformations, in that they are either employed 



materials and j n fa Q manner described above for the formation of plastic 



the products 



of the destruc- material, and thus for building up new cell substance; or 



un( l er g the destructive tissue change in which they 

 are destroyed by the respiration, and in part converted 

 into materials which can no longer serve as nutrient 

 material, and which must be got rid of as excreta. Just 

 as in the tissue change of animals, it is not by any means 

 necessary to assume that all the assimilated materials 

 form in the first place cell substance and afterwards 

 undergo destruction; it is, on the contrary, probable that 



