3o8 DISEASES OF CULTIVATED PLANTS 



Uredospores irregularly globose, aculeate, ochraceous 

 brown, apex thickened, 23-38 X 20-26 /x, with two germ-pores. 



Teleutospores often deformed, slightly constricted at the 

 septum, both ends rounded, smooth, brown, apex thickened, 

 30-56 x 17-28/*. 



Dilute Bordeaux mixture checks the spread of the disease. 

 Diseased leaves should be removed. 



Puccinia obtegens (Tub.), better known in this country under 

 the erroneous name of Puccinia suaveoleits (Pers.), is exceed- 

 ingly common on the field thistle (Cnicus arvensis, Hoffm.). 

 The mycelium of the fungus hibernates in the rootstock of 

 the host-plant, hence when a plant is once infected it remains 

 diseased for all time. Diseased plants appear earlier in the 

 season than healthy ones, and are readily recognised by the 

 sickly pale green colour of the leaves, which grow upright 

 showing the under surface. No flowers are produced. The 

 spores emit a pleasant odour when the leaves are rubbed 

 between the fingers. As diseased plants do not produce seed, 

 by infecting sound plants, which is readily effected by lashing 

 them with a diseased plant when damp, it should be possible 

 to eradicate one of our worst weeds. 



Hemipuccinia. Uredospores and teleutospores produced 

 on the same host ; aecidia and spermogonia absent. 



Sunflower rust [Puccinia /anaccti, D. C.) forms brown 

 pustules on the leaves of the sunflower {Helianthus annuus) 

 and on tansy ( Tanacetum). The rust is sometimes so abundant 

 as to destroy the foliage. 



Uredospores elliptic or ovate, 19-35x16-25 /*, minutely 

 aculeate, ochraceous. 



Teleutospores elliptical or ovate, apex much thickened, 

 cells almost equal, constricted at the septum, smooth or the 

 apex granulated, chestnut brown, 32-60x17-28 /i, pedicel 

 long. 



Bordeaux mixture has been proved to check the disease. 



Plum leaf rust {Puccinia pn/ni, Pers.) is very prevalent 

 on the leaves of cultivated plum trees, cherry, peach, apricot, 

 almond, and also on the blackthorn. According to M 'Alpine 

 it also occurs on twigs and fruit. The uredo and puccinia 

 stages form numerous small brown spots on the under surface 

 of the leaf, which is often almost entirely covered with the 

 rust. The disease spreads very quickly under favourable 



