. Nature and development of plants. Botany. 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, an). In the majority of the species, singularly enough, the female gametes germinate without being fertilized. The gametospore germinates as in Vauc
. Nature and development of plants. Botany. 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, an). 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-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of the
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