220 REPRODUCTION OF A WATER MOULD 



the gametes is perhaps due to their exposure to atmospheric 

 conditions, as would be the case when growing upon terrestrial 

 or floating organic matter. The lack of water for the transport 

 of the male gametes is nicely met by a tubular outgrowth of 

 the antheridium which penetrates the oogonium when it ruptures, 

 discharging the male close to the female gametes (Fig. 130, D, 

 a?i). In the majority of the species, singularly enough, the female 

 gametes germinate without being fertilized. The gametospore 

 germinates as in Vaucheria. 



It should be stated that, in related forms, large multiciliate 

 zoospores, like those of Vaucheria, are formed and also motile 

 male gametes. It is also important to note that there are several 

 parasitic algae closely related to these alga-like fungi and this 

 remark applies to the Sac Fungi as well. Their parasitic habit 

 and partial loss of chlorophyll clearly indicate that they are in a 

 transition state from the algae to the fungi. It is therefore 

 safe to state that in this group we have evidence of the derivation 



Fig. 131. Hyphae of Peronospora extending through the tissues of a plant 

 and absorbing food from the cells by means of haustoria, h. 



of the fungi from the algae. This helps us to understand how 

 fungi arose. Plants and animals live upon organic materials. 

 These substances through chemical and physical reactions cause 

 the absorbing organs of the plant to grow towards them. Conse- 

 quently the green plant though capable of forming organic sub- 

 stances may through chemical stimulation be brought into con- 

 tact with these materials in other plants and animals and as a 

 result it becomes a fungus. 



79. Order b. Peronosporales. Downy Mildews and White 

 Rusts. — These forms are parasites upon the higher plants espe- 



