PART 111. THE CLASSIFICATION OF PLANTS. 



The male and female sexual organs are commonly borne on the same hypha, 

 but in some cases (e.g. Saprolegnia dioica and anisospora) this is not the case ; 

 however, it is not clear that these species are actually dioecious. In some 

 species (Saprolegnia Thureti, torulosa, monilifera, and Achlya stellata) no male 

 organs are developed as a rule ; in others (Saprolegnia mixta, Achlya spinosa) 

 they are as often absent as present; in others they are frequently absent 

 (Aphanomyces stellatus, Saprolegnia hypogyni, Aplanes Braunii) ; in others, 

 finally, they are always present (Achlya racemosa and polyandra, Saprolegnia 

 monoica). 



When pollinodia are present, they are closely applied to the oogonium ; 

 sometimes several are applied to one oogonium. In some forms (e.g. Sapro- 

 legnia asterophora) the pollinodium undergoes no change, or it sends out a 

 short tube which enters the oogonium but does not touch the oospheres. In 

 most others the pollinodium sends out one or more tubes which enter the 

 oogonium and come into close contact with the oospheres. But in all cases 

 the tubes remain closed, and no act of fertilisation has been observed. The 

 oospheres, however, all become oospores ; but since there is apparently no 

 fertilisation, this change is produced parthenogenetically. 



The germination of the oospores presents the same variations as in the 

 Peronosporaceae. The life-history of the Saprolegniaceffi is therefore essentially 

 the same as that of the Peronosporacea? . 



The principal genera are Saprolegnia, Achlya, Aphanomyces, Dictjucbus, 

 Aplanes, Apodya. 



Sub-Class IV. ASCOMYCETES. This sub-class includes a 

 vast number of forms, both saprophytes and parasites. Some of 

 them (e.g. Penicillium glaucum, Eurotium Aspergillus) are familiar 

 as the blue or green moulds appearing on jam, old boots, etc. ; 

 others (Erysiphese) as mildew on roses, etc : Cordyceps infests 

 the larvae of insects. 



On the assumption of the sexuality of the Ascomycetes (see p. 

 279), the life-history of typical members of this group presents a 

 well-marked alternation of generations ; the plant is the gameto- 

 phyte; the ascocarp is the sporophyte; an alternation which is 

 the same as that of the Rhodophyceae among the Algae. The 

 similarity is further emphasised by the fact that, as in the 

 Rhodophycese, the gametophyte may be potential. In some cases 

 the life-history is complicated by the polymorphism of the game- 

 tophyte, which includes in its life-history one or more entirely 

 asexual gonidia-bearing forms. These various life-histories are 

 briefly illustrated by the following examples. 



1. The gametophyte produces no gonidia (e.g. Eremascus albus, 

 Gymnoascus, most Ascomycetous Lichen-fungi, Ascobolus furfur- 

 aceus, Pyronerna). In these the life-history is perfectly simple, 



