216 DISEASES OF CULTIVATED PLANTS 



The Septoria usually forms many rather small, irregularly 

 rounded spots on the living leaves, these become dry and 

 greyish, surrounded by a brown border, and are most con- 

 spicuous on the upper surface of the leaf. The perithecia, 

 resembling minute black dots, are thinly scattered over the 

 diseased spots on the under side of the leaf. 



Perithecia of conidial form, globose, sunk in the tissues of 

 the leaf; conidia long and slender, slightly curved, 3-celled, 

 hyaline, escaping from the perithecium in the form of a viscid 

 tendril, 60X3-4 /*. 



Perithecia of ascigerous form are globose and immersed, 

 with a short, slightly projecting mouth. Asci 60-75 X 11-13 /*, 

 8-spored; spores hyaline, very slightly curved, fusiform, 

 i-septate, 26-33x4 /*. 



Spray with half strength Bordeaux mixture, beginning 

 when the foliage is quite young. Diseased, fallen leaves 

 should be destroyed. 



Klebahn, Zeit. Pflanzenkr., 18, p. 5 (1908). 



Elm leaf spot. Numerous small brown spots appear on 

 the under surface of the leaves, which in consequence gradu- 

 ally turn yellow and fall early in the season. The minute 

 spores ooze to the surface of the leaf in white, viscid tendrils, 

 and if not washed off by rain, adhere to the surface of the 

 leaf, which is then sprinkled with minute whitish patches. 

 Until recently it was supposed that this disease was entirely 

 due to Phleospora u/mi, Wallr. (at one time Septoria 

 ulmi, Fr.), whose spore-clusters are produced in the tissue 

 of the leaf underlying the brown spots. The spores 

 are narrowly fusiform, slightly curved, 2-4-septate, 25-50 x 

 4-7 /* Quite recently, however, Klebahn has shown that 

 Phleospora is only a conidial form of an ascigerous fungus, 

 called Mycosphaerella ulmi (Klebahn). This stage of the 

 fungus develops on dead leaves in the spring ; the flask-shaped 

 perithecia are embedded in the tissue of the leaf. The asci 

 contains eight spores in two rows. Spores hyaline, i-septate, 

 subfusiform, 22-27x4-5^. 



Parasitic on Ulmus campestris and other species of Ulmus. 



Nursery stock and young trees suffer most from this 

 disease. Spray with Bordeaux mixture, and collect and burn 

 fallen leaves. 



Klebahn, Pringsh. Jahrb., 1905, p. 485. 



