FUNGI. 



69 



appears surrounded by a single layer of cells, sufficiently transparent, 

 however, to allow a view of the interior. 



The antheridiuni undergoes no further change, but the archicarp soon 

 divides into two cells, a small basal one and a larger upper cell. There 

 next grow from the inner surface of the covering cells, short filaments, 

 that almost completely fill the space between the archicarp and the wall. 

 An optical section of such a stage (Fig. 39, F) shows a double wall and 

 the two cells of the archicarp. The spore fruit now enlarges rapidly, and 

 the outer cells become first yellow and then dark brown, the walls becom- 

 ing thicker and harder as they change color. Sometimes special filaments 

 or appendages grow out from their outer surfaces, and these are also dark- 



FIG. 41. Forms of mildews (Erysiphe). A, Microsphsera, a spore fruit, x 150. 

 B, cluster of spore sacs of the same, x 150. (7, a single appendage, x 300. 

 D, end of an appendage of Uncinula, x 300. E, appendage of Phyllactinia, 

 x 150. 



colored. Shortly before the fruit is ripe, the upper cell of the archicarp, 

 which has increased many times in size, shows a division of its contents 

 into eight parts, each of which develops a wall and becomes an oval spore. 

 By crushing the ripe spore fruit, these spores still enclosed in the mother 

 cell (ascus) may be forced out (Fig. 39, H). These spores do not germi- 

 nate at once, but remain dormant until the next year. 



Frequently other structures, resembling somewhat the spore fruits, are 

 found associated with them (Fig. 39, /, A'), and were for a long time sup- 

 posed to be a special form of reproductive organ ; but they are now known 

 to belong to another fungus (Cicinnobulus), parasitic upon the mildew. 

 They usually appear at the base of the chains of conidia, causing the basal 

 cell to enlarge to many times its original size, and finally kill the young 



