82 FIRST GROUP. THALLOPHFTES. 



their way into the plants or animals which supply them with nourishment in 

 various ways; sometimes they pierce through the outer skin, sometimes they 

 enter by the stomata. Many Fungi, as Ustilago, make their way into the plant 

 only in its earliest stage and then grow luxuriantly throughout the growing plant ; 

 the greater number are not limited to any definite stage in the life of their host. 

 There are Fungi living a peculiar kind of life, that cannot be called parasitic, in 

 association with other organisms which contain chlorophyll and therefore assimilate 

 carbon; these, together with the Algae round which they weave their hyphae, 

 form a large and very distinct class of Thallophytes, the Lichens. This social life 

 of Fungi with Algae is called by De Bary symbiosis J , and will be described at greater 

 length below. The great majority of Lichen-fungi belong to the section Ascomycetes, 

 but it has been recently shown that a Basidiomycete is the Fungus in the Lichen- 

 genus Cora. 



The Fungi, like the Algae, have as a class both sexual and asexual propa- 

 gative cells; but a large number of Fungi have only the asexual forms (gom'dia, 

 com'dia); in some there occur peculiar phenomena of abortion in the sexual 

 organs, and in many species, as in the Uredineae, the sexual process is not yet 

 cleared up 2 . The branches of a hypha that has proceeded from the germination 

 of a propagative cell usually manifest a division of labour; some penetrate into 

 the substratum and spread abroad there in search of food, while the others grow 

 at the expense of the organs from which they sprang. The hyphae which spread in 

 the substratum as organs for obtaining food form the mycelium (spawn), and 

 answer as regards their function to the root-like structures (rhizoids), for example, 

 of Chara. If special branches of the hyphae serving for reproduction are present 

 on the mycelium, they are called carpophores. Both the mycelial threads and the 

 carpophores may be simple hyphae, as in the Filamentous-fungi, or a number of 

 hyphae and their branches unite into a closely-woven tissue and form compact bundles 

 of filaments, :he individual elements in which are more or less intimately associated 

 by the union of their walls. For instance, the large asexual carpophores (fructifica- 

 tions) of the Cap-fungi or Mushrooms, ordinarily regarded as the whole Fungus 

 because the slender mycelium is hid in the substratum, are formed of interwoven 

 hyphae. Agaricus melleus mentioned above has bundles of mycelial filaments formed 

 by the union of many individual hyphae, which were supposed to be a distinct genus, 

 Rhizomorpha, before it was recognised that they belonged to Agaricus melleus. 

 Similar bundles though less conspicuous occur in many other Fungi. The peculiar 

 bodies named sclerotia, resting states of the mycelium found in many Fungi, are 

 formed in the same way. These sclerotia are small tuber-like bodies of varying size, 

 which are able to remain for some time in a dormant condition and especially to 

 withstand the effects of desiccation, and then under more favourable conditions to 

 enter on a further course of development. They consist of a cortical layer and an 

 inner compact tissue, with cell-walls that are often thick and of a cartilaginous con- 

 sistence, so that their origin from separate hyphal branches woven together is 

 often no longer perceptible in the mature state. Another kind of union of the 



1 [Lichens illustrate one form of symbiosis only. The term is applicable to all conditions in 

 which dissimilar organisms live together.] 



2 [See Marshall Ward, On the Sexuality of the Fungi (Q. J. M. S. April, 1884).] 



