306 H. MARSHALL WAED. 



when cross fertilised — we may suppose that at length the 

 Fungus derives too little benefit to be able to go on^ or the 

 season during which the host plant flourishes is drawing to 

 an end. 



No doubt we have in heteroecism the salvation of such a 

 Fungus. Not only is it carried through a dangerous period, 

 by seeking relief at the hands of a second host, but — and which 

 I believe to be far more important — it obtains re-invigoration 

 by the new protoplasm with which it comes in contact. We 

 may not inaptly compare the sojourn of the Fungus on its 

 second host, to a trip to the seaside, where the weary and 

 enfeebled organism enjoys fresh diet and associations for a 

 time, which in their turn pall and prepare the recipients to 

 renew old modes of life. 



We have seen that the disappearance of the sexual organs, 

 leading to apogamy, commences especially in the lower 

 Ascomycetes, and it may be more than a coincidence that 

 epiphytic forms, which show a tendency to produce one kind of 

 spore while on the living leaf and develope their asci on the 

 fallen leaf are common here ; such forms suggest how the 

 parasitism and heteroecism of higher forms may have begun, 

 and it is remarkable that the apogamy becomes more and 

 more complete as we ascend through the latter. 



It is not pretended that the hypothesis embodied above at 

 once explains all the cases possible, and it will be well to state a 

 few of the greater difficulties at once. The Basidiomycetesl 

 shall not dwell upon, since our knowledge of them is still very 

 imperfect. The few cases of pai-asitic Basidiomycetes known 

 can hardly be cited as supporting the view adduced ; and if it 

 turns out that all the forms are as utterly devoid of sexuality 

 as Brefeld's C op r in us, and that no other generation exists 

 than the one now known, it will be difiicult or impossible to 

 reconcile the facts, and the coincidences referred to in this 

 essay may have to be accepted as coincidences only. 



Apart from this, the difficulty must suggest itself to many 

 that there are parasitic Fungi — such as the Peronosporeje — 

 which nevertheless develope the sexual organs in the condition 



