364 FUNGI 



For example, the acrospore form called Oidium Tuckeri (Berk.), which, 

 occurs abundantly, and is well known as vine-mildew, never produces in 

 Europe, so far as is known, peritheces. These it is beHeved have been 

 found on native vines in North America, which is supposed to be the 

 home of the disease, the perithecial form being the fungus described as 

 Erysiphe (Uncinula) spiralis (Berk, et Curt.). 



The Erysiphese are parasites infesting living flowering plants of many 

 natural orders. Among the best known and most destructive are the 

 above-mentioned vine-mildew j E. lamprocarpa (Lk.) on Compositae, . 

 Plantago, Verbascum, Labiate ; E. graminis (Lev.) on grasses ; E. 

 Martii (Lev.) on Umbelliferae, clover, lucern, lupins, &c. ; E. communis 

 (Lk.) on Polygonum, Rumex, Convolvulus, Dipsacus, Lathyrus, 

 Delphinium, Aquilegia, Ranunculus, &c. Podosphsera Kunzei (L6v.) 

 attacks species of Prunus, and Podosphaera Castagnei (de By.) is a well- 

 known mildew of hops, though it also ,■ attacks many other plants of 

 different natural orders. 



2. EuROTiUiM (Link). — The carpogone is formed by the rolling up 

 in corkscrew fashion of the tip of a mycelial hypha, the turns of which, 

 four or five in number, gradually come into closer contact till they pre- 

 sent the appearance of a hollow screw. It is then divided by transverse 

 walls into as many cells as there are turns in the screw. From the 

 bottom turn of the screw there grow up two or three branches of irregular 

 diameter, which take an irregular course towards the apex, but remain 

 in close contact with the outside of the carpogone. Sometimes one 

 ascends bj' way of the inside of the screw. One, however, climbs faster 

 than the others and reaches the apex first ; this is the antherid. Im- 

 pregnation by it having taken place at the apex of the carpogone after 

 the absorption of a minute portion of the wall, both the antherid and 

 the other branches of the basal turn of the carpogone which follow it 

 proceed to branch copiously, the hyphse being septate, until the carpo- 

 gone is completely enveloped. In this way the outer perithecial wall 

 is formed as in the Erysiphes. From it, as in the last type too, the 

 inner wall grows inward, filling up the space between the outer wall and 

 the carpogone with several layers, and pressing apart the turns of the 

 screw. The wall-cells are of a pseudo-parenchymatous appearance, and 

 the membrane of the outer wall becomes covered externally by a 

 golden-coloured substance. The whole of these envelope-cells, it should 

 be mentioned, increase in volume considerably. From the carpogone 

 there now proceed numerous ascogenous hyphee, which press among and 

 suppress the inner wall-cells, and, branching plentifully, bear at the ends- 

 of the branches oval asci. These contain each eight ascospores. Sa 

 copiously does this take place that, of the ascogenous hyphae soon only- 



