310 



CLASS ASCOMTCETEAE 



the young shoots, the buds, fruits, etc. Sphaerotheca phytoptophila Kell. & 

 Swingle is found only on the lobed galls produced on the hackberry (Celtis 

 occidentalis L.) by a species of mite. Vncinula necator (Schw.) Burr, 

 attacks not only the leaves and young green shoots but also the immature 

 berries of the grape (Vitis) while Sphaerotheca mors-uvae (Schw.) B. & C, 

 on the gooseberry (Grossularia) is more often on the berries. The mycelium 

 is mainly superficial, obtaining its nourishment by haustoria penetrating 

 the epidermal cells or even to the cell layer immediately underneath. In 

 Phyllactinia part of the mycelium enters the stomata and sends its 



Fig. 98. Erysiphales, 

 Family Erysiphaceae. Ery- 

 siphe graminis DC. Conidio- 

 phore and chain of conidia 

 arising from surface my- 

 celium. (After Salmon: Mem. 

 Torrey Botan. Club, 9:1- 

 292.) 



haustoria into the mesophyll cells bordering the substomatal chambers. 

 In Leveillula the mycelium enters the leaf through the stomatal opening 

 and is confined to the mesophyll except that the conidiophores emerge 

 through the stomata. Foex (1912) pointed out that from this interior 

 mycehum there eventually creeps out through the stomata a thin myce- 

 lium growth which spreads out over the epidermis, held fast to it by 

 appressoria, but not producing any haustoria. This external mycelium 

 produces the perithecia and a few conidiophores bearing short chains of 

 small conidia which are smaller than those borne singly on the conidio- 

 phores emerging from the stomata. The mycelial cells are always uni- 

 nucleate. The conidia arise at the apex of short or elongated conidiophores. 

 In Leveillula and Phyllactinia the conidium falls off before the next suc- 

 ceeding conidium is formed, but in the remaining genera of the family the 

 conidia remain attached so that a chain of conidia is produced which in 



