68 BOTANY. 



much- interlaced filaments, divided at intervals by cross-walls. 1 They are 

 nearly colorless, and the contents are not conspicuous. These filaments 

 send up vertical branches (Fig. 39, A), that become divided into a series 

 of short cells by means of cross- walls. The cells thus formed are at first 

 cylindrical, but later bulge out at the sides, becoming broadly oval, and 

 finally become detached as spores (conidia). It is these spores that give 

 the frosty appearance to the early stages of the fungus when seen with the 

 naked eye. The spores fall off very easily when ripe, and germinate 

 quickly in water, sending out two or more tubes that grow into filaments 

 like those of the parent plant (Fig. 39, B). 



The spore fruits, as already observed, are formed toward the end of the 

 season, and, in the species under consideration at least, appear to be the 



result of a sexual process. The sex- 

 ual organs (if they are really such) 

 are extremely simple, and, owing to 

 their very small size, are not easily 

 found. They arise as short branches 

 at a point where two filaments cross ; 

 one of them (Fig. 39, <7, ar.), the fe- 

 male cell, or "archicarp," is some- 

 what larger than the other and nearly 

 FIG. 40. Chrysanthemum mildew ! . fmnY1 nTW i ____. hooc 

 (Erysiphe), showing the suckers OVal m 10rm ' and SOOn becomes 

 (h) by which the filaments are at- separated by a partition from the fila- 

 tached to the leaf. A surface men t that bears it. The other branch 

 view. 5, vertical section of the . ., .,. x 



leaf, x 300. (antheridium) grows up in close con- 



tact with the archicarp, and like it is 



shut off by a partition from its filament. It is more slender than the 

 archicarp, but otherwise differs little from it. No actual communication 

 can be shown to be present between the two cells, and it is therefore still 

 doubtful whether fertilization really takes place. Shortly after these 

 organs are full-grown, several short branches grow up about them, and 

 soon completely envelop them (l>, E). These branches soon grow to- 

 gether, and cross-walls are formed in them, so that the young spore fruit 



1 The filaments are attached to the surface of the leaf by suckers, 

 which are not so readily seen in this species as in some others. A mildew 

 growing abundantly in autumn on the garden chrysanthemum, however, 

 shows them very satisfactorily if a bit of the epidermis of a leaf on which 

 the fungus is just beginning to grow is sliced off with a sharp razor and 

 mounted in dilute glycerine, or water, removing the air with alcohol. 

 These suckers are then seen to be globular bodies, penetrating the outer 

 wall of the cell (Fig. 40). 



