620 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



plants, which were stunted and presented a yellowish appearance, 

 could be distinguished from the healthy ones at a glance. The leaves, 

 which were sometimes half -folded or curled, were marked, sometimes 

 quite thickly, with dark brown patches, much smaller and darker than 

 those caused by Phytophthora infestans. 



In many instances, when examined closely, the blotches possessed 

 a dark brown centre, sometimes only a spot, surrounded by a margin 

 of a lighter shade. This is shown in the illustration, which is a draw- 

 ing from a preserved and flattened specimen obtained in September 

 (fig. 181). Sections were made across the blotched areas of leaves 

 collected in September, and it was found that the epidermal cells of 

 both the upper and lower surfaces were diseased and discoloured. The 

 guard cells of the stomata were, on the whole, badly affected. The 

 disease frequently extended inwards from the epidermal cells to the 

 palisade tissue and mesophyll, and sometimes reached the vascular 

 bundles, but there was no evidence to show, from the specimens 

 examined, that it proceeded and spread from the bundles to the 

 mesophyll and superficial cells. The condition of the conducting 

 tissues of the petioles of diseased leaves was not such as to lead one 

 to suppose that the disease had passed from the stem into the petiole 

 and thence into the leaflets by means of the bundles. Several kinds 

 of fungus-spore were observed upon the surfaces of leaves collected 

 late in the season, amongst which were those of the form known as 

 Macrosporium. 



It is not advisable to draw conclusions with respect to the effect 

 produced upon the plant owing to the condition of the guard cells ; nor 

 is it safe to speculate as to the nature and habit of the organisms * 

 present from a study of the late stages of the disease only. 

 It is hoped to deal with this subject when the matter has been more 

 fully investigated. 



Vanha,f in 1904, described a potato disease — Potato-leaf Blotch— 

 which he supposed to be due to the fungus Sporidesmium solani varians 

 Vanha. The foliage of plants affected with this disease is disfigured 

 owing to the occurrence of small, scattered, brown spots on the leaves. 

 These spots increase in size and fuse together, forming well-defined 

 blackisli-brown patches. Several forms of spore, including Macro- 

 sporium, are said to be produced during the life-cycle of Sporidesmium. 

 Massecj states that this disease has only quite recently been observed 

 in Britain. 



Massee attributes a form of potato-leaf curl to Macrosporium 

 solani Cooke. He states that the leaves curl, and that the stem droops 

 before there is any external evidence (blackish-olive patches) of the 

 cause of injury, and that as soon as the leaves begin to curl a micro- 

 scopic section of the stem shows a dense mass of mycelium which 

 plugs the water- conducting parts. ** At a later stage, however, the 



* The reproductive bodies of an animal organism were found in the diseased 

 tissue of the particular specimens examined. 



t Vanha. Mittcil. Landesl.-VersucJist. fiir Pfianzenkr., Brunn II. (1904). 

 X Cr. Massce, Diseases of CuUivatcd Plants and Trees, p. 499. 



