66 MANUAL OP BOTANY 



Class II.— FUNGI. 



This class of ThaUophytes differs from the preceding one 

 especially by the absence of chlorophyll from the tissues of 

 the plants which it comprises. In other respects there is 

 a great similarity between the two groups. The absence of 

 chlorophyll, however, makes such a material difference to the 

 mode of nutrition, and leads ultimately to such great differences 

 in degree of development, that they are properly separated into 

 two distinct classes. The fungi cannot assimilate the CO., of 

 the atmosphere, and are therefore compelled to obtain their 

 carbonaceous food from somewhat complex compounds, which 

 have, however, a. fairly wide distribution. Some fungi obtain 

 them from other living organisms, both anunals and vege- 

 tables, on which they prey, their tissues entering into the 

 living substance of their hosts and absorbing therefrom the 

 food-stuffs they need. These are called parasites. Others 

 grow upon decaying organic matter, either in the soil or else- 

 where ; these are known as saprophytes. Yet a third class 

 exists, whose members live in intimate relationship with living 

 green plants, the two forming together a complex organism, 

 partly chlorophyllaceous, partly fungal, the two constituents 

 playing each its own part in the nutrition of the whole. Such a 

 mode of Ufe is called symbiosis ; it differs from parasitism in 

 that the fungus does not in any way injure the green plant with 

 which it is in such close relationship. The best examples of 

 symbiosis may be found in the next class, the Lichens, where an 

 alga and a fungus live together. In this it is illustrated by the 

 micorhiza found on the roots of many of our forest trees. 



In their life history the fungi show an alternation of genera- 

 tions, but not at aU a regular one. Many species have both 

 gametophyte and sporophyte phases, but these rarely if ever alter- 

 nate with constancy. The gametophyte is always the larger and 

 most important form, the sporophyte being sometimes repre- 

 sented only by the oospore or zygospore, sometimes by a small 

 2JromyceKum developed from it, sometimes by a kind of fructifi- 

 cation recalling the cystocarp of the red Algise. The gametophyte 

 usually bears spores or gonidia in addition to the gametes ; indeed 



