Morphology and Life-History 5 



walled, one-to-many septate, about ion thick, and ft-om no to 

 380/^ high. From these the conidia are formed by abstriction, 

 either singly at the apex or in long' chains in basipctal succes- 

 sion. The conidia are continuous, /. e., non-septate, colorless or 

 white, oblong, cyhndrical, or barrel-shaped, smooth, thin-walled, 

 and from 20-50 X 10-24 /i in size. Harper (161, p. 664) states 

 that a single nucleus passes from the parent-hypha into the young 

 conidiophore, and that from it arise the nuclei of all the conidia 



subsequently formed. 



Conidial forms of the Erysiphaccae were formerly classified as an 

 autonomous genus of the Hyphomycctcs under the name of Oiditim. 

 It soon became observed, however, that the Oidium was frequently 

 succeeded by species of the Erysiphaccae, or that the Oidium 

 even occurred among the perithecia of the latter. Berkeley In 1841 

 (26, see also 29) was among the first to give couclusive evidence 

 of the organic connection of the Oidium with the Erysiphaccae. 

 It is now well known that during the stage in which the conidial 

 form is just passing over Into the perithecial, conidlophores and 

 perithecia may frequently be observed in organic connection. 

 ■ The conidia are usually formed in immense numbers through- 

 out the summer, and being easily carried by the wind, are the means 

 of rapidly spreading the fungus during the growing season. It 

 may be noted that Wagner (380) observed in several Instances the 

 distribution of conidia effected by snails, and mentions that the 

 conidia oi Erysiphe polygoni on plants oi Hypericum by this means 

 were carried to plants of Aquilegia, and those of Sphacrotheca 

 Castagnci on Impaticns to other plants (sec also Stevens (340*) )- 



The conidia are capable of immediate germination on reaching 

 the epidermis of a suitable host-plant. Even in a dry atmosphere, 

 but more readily In a damp one, or in water, one or more delicate 

 germinal tubes are produced near one end of the conidium. Soon 

 the first haustorium is formed (sometimes immediately on ger- 

 mination), and from this center hyphae grow out, branching, 

 crossing, and developing haustoria. ' The vegetative mycelium 

 thus formed continues to develop, and under favorable conditions 

 begins to produce conidia in a few days. 



*Dangeard (96) has observed cases of conidiophores being produced direct from 

 the genninating conidium. 



