ALG^E-FUNGI 



187 



The formation of resting-spores of vaucheria is accomplished 

 by means of special organs, oogonia Fig. 342. o, and antheridia. (Fig. 

 342, a.) Both of these are specially developed branches from the thallus. 

 The antheridia are nearly cylin- 

 drical, and curved toward the 

 oogonia. The upper part of an 

 antheridium is cut off by a 

 cross-wall, and within it nu- 

 merous ciliated sperm-cells are 

 formed. These escape by the 

 ruptured apex of the antherid- 

 ium. The oogonia are more enlarged than the antheridia and have 

 a beak-like projection turned a little to one side of the 

 apex. They are separated from the thallus-thread by a 

 cross-wall, and contain a single large green cell, the egg- 

 cell. The apex of the oogonium is dissolved, and through 

 the opening the sperm-cells enter. Fertilization is thus 

 accomplished. After fertilization, the egg-cell becomes 

 invested with a thick wall and is thus converted into a 

 resting-spore, the odspore. (Fig. 343.) 



342. Thread of vaucheria with oogonia 

 and antheridia. 



FUNGI 



Some forms of fungi are familiar to every one. Mushrooms and 

 toadstools, with their varied forms and colors, are common in fields, 

 woods and pastures. In every household the common moulds are 

 familiar intruders, appearing on old bread, vegetables and even within 

 tightly sealed fruit jars, where they form a felt-like layer dusted over 

 with blue, yellow or black powder (192). The 

 strange occurrence of these plants long mystified 

 people, who thought they were productions of the 

 dead matter upon which they grew, but now we 

 know that a mould, like any other plant, cannot 

 originate spontaneously; it must start from some- 

 thing which is analogous to a seed. The "seed" 

 in this case is a spore. The term spore is applied 

 to the minute reproductive bodies of all flower- 

 less plants. A spore is a very simple structure, 

 usually of only one plant-cell, whose special 

 function is to reproduce the plant. A spore may 

 be produced by a vegetative process (growing out from the ordinary 

 plant tissues), or it may be the result of a fertilization process (344). 



344. Mucor mucedo, 

 showing habit. 



