FUNGOID PESTS OF CULTIVATED PLANTS. 37 



when held to the light, pellucid dots are seen scattered irregularly over 

 the leaf. After a time the dots show a distinct spot, and as the disease 

 extends inside the leaf the surface tissues dry, the internal tissues col- 

 lapse, and whitish sunken spots appear. As the spots enlarge the leaves 

 wither. Very badly diseased plants have more yellowish-green leaves 

 than normal. The lower leaves die prematurely, and the vitality of the 

 plant is lowered so as to check growth -and decrease flowers. 



The disease is caused by parasitic bacteria entering the plant from the 

 air. The germ associated with the disease may be separated and shown, 

 by artificial infection of healthy plants, to be the cause of the disease. 

 The cells are described as elliptical, single, or rarely united (f-1 J x 1-2 /j.), 

 in fluid media more united, forming short filaments, afterwards elongated 

 and convoluted zooglaea. 



Plants may be kept essentially free from the disease by keeping the 

 foliage dry, and preventing the presence of aphides. Unfortunately we 

 examined British-grown plants affected badly by the disease in February 

 1902. 



Purdue University Exp. Station Bull. 59, March 1896 ; Bacteriosis 

 of Carnations, by J. C. Arthur and H. L. Bolley ; Journ. B.H.S. 1902, 

 p. 653 ; xxviii., 1904, p. 713. 



MALLOW LEAF- SPOT. 

 Phyllosticta destructives (Desm.), PI. II. fig. 41. 



This form of leaf -spot is common enough on all the uncultivated 

 Mallows, and sometimes finds its way into gardens on nearly any kind 

 of malvaceous plant. It makes the foliage very unsightly, since the 

 tissue of the spots falls out, and leaves ragged holes in the leaves. 



The spots are somewhat rounded, of a pale ochrey colour, surrounded 

 by a darker line. The perithecia, like little dots, are often in concentric 

 rings, but the whole dead tissue of the spots is brittle, and soon crumbles 

 away. 



The sporules are oblong, with two nuclei, and are expelled from the 

 mouth of the perithecia in flesh-coloured tendrils. 



It is known in France, Belgium, Italy, and Austria. 



Sacc. Syll. iii. 814 ; Grevillea, xiv. p. 73. 



Another leaf-spot (Phyllosticta altheind) is found in France and Italy 

 on Hollyhock leaves, and one, Phyllosticta althaicola, on the Marsh 

 Mallow in France. One of the species with two-celled sporules, Ascochyta 

 parasiiica, favours the Hollyhock in France, and one with long thread- 

 like sporules (Septoria parasitica) accompanies it on the same plants. 



Septoria heterochroa (Desm.) (Cooke Hdbk. No. 1313) is found on 

 leaves of uncultivated Mallows. 



HOLLYHOCK BRAND. 

 Puccinia Malvacearum (Corda), PL III. fig. 42. 



This was at one time one of the most dreaded enemies of the Holly- 

 hock, which suddenly made its appearance on the leaves of all malvaceous 

 plants, and spread with extraordinary rapidity all over the country. It 



