TOO Elementary Biology. 



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Amongst Fungi, then, for the first time we meet with 

 what is known as altercation of generations between an 

 asexual and a sexual condition a phenomenon which we 

 shall find lies at the base of all knowledge of the life-histories 

 of the higher plants. 



It will be seen that the asexual method of multiplication 

 is much the more efficient of the two, inasmuch as it is in- 

 finitely simpler, waste of reproductive cells is not of so much 

 moment, their formation takes up a very short space of 

 time, and they are, at least for many generations, quite as 

 fertile as the true products of sexual union. It is con- 

 ceivable that under these circumstances the sexual method 

 of multiplication might in the Fungi fall into disuse and 

 ultimately disappear altogether. Hence arises the phe- 

 nomenon of apogamy in Fungi, i.e. the absence of sexual 

 reproductive powers. We have all stages in the degenera- 

 tion exemplified by different forms. We have instances, for 

 example, of male and female organs being formed which 

 never unite, of dwarf male organs which perform apparently 

 no function, and of forms like the common mushroom 

 (Agaricus}, where, so far as we know, no sexual organs are 

 formed at all. Apogamy is especially interesting when viewed 

 in relation to the life-history and habits of these plants. 



A physiological classification of Fungi into two groups 

 may be formulated, based on their habits. Some live on 

 dead or decaying organic matter ; such are termed sapro- 

 phytes ; others live parasitically on living plants and 

 animals usually causing a more or less serious disease in 

 the host ; such forms may be termed parasites. As a 

 general rule, it may be laid down that the more pronounced 



1 The colonial habit of the moulds accounts for the co-existence of 

 the two generations on the same plant. A thallus may bear in one 

 place sexual reproductive organs, in another spore-producing filaments. 



