Pethybridge &, LAffkrtv — Disease of Tomato and other Plants. 4$9 



and be treated as " cuttings," many of them throw out a fresh set of adventi- 

 tious roots, and develop into healthy, useful plants. 



The primary root-system of an affected plant is usually badly decayed or 

 entirely rotten. Evidently stimulated by the loss of these roots, the plant 

 attempts to combat the attack of the parasite by developing a system of 

 secondary, adventitious roots from the still healthy base of the stem higher 

 up. But these also in turn become attacked ; and finally the plant dies. It 

 is, therefore, characteristic of this disease to see the older roots dead and 

 decayed, and to find a bunch of adventitious roots formed above them, some 

 of which may also be in process of being killed. 



Essentially, then, the disease takes the form of a more or less rapidly 

 progressing rot of the root system in which a portion of the base of the stem 

 also becomes involved ; and if a popular name for the disease be demanded, 

 the term "tomato foot-rot" may, perhaps, be regarded as not unsuitable for 

 it. A typically affected young plant is illustrated in fig. 1, PL Xl/V. 



The rapidity with which death supervenes appears to be closely correlated 

 with the age of_ the plant when first attacked; but it is doubtless also 

 influenced by the conditions of temperature and moisture, both of soil and 

 atmosphere, under which the plants are being raised. If infection occurs 

 when the seedlings are young, death rapidly ensues; but if the plants are 

 older, their struggle for existence is more prolonged. 



On cutting the base of the stem of an infected plant longitudinally it is 

 seen that the parts most involved in the rot are the soft parenchymatous 

 tissues surrounding and surrounded by the wood. Microscopical prepara- 

 tions show the presence of comparatively abundant thin-walled, branched 

 non-septate hyphae, of relatively large diameter, traversing these tissues both 

 intra- and inter-cellularly. Where these hyphae invade still healthy tissue, 

 however, they travel only between the cells. In very young seedlings 

 hyphae of a similar kind were sometimes observed running longitudinally in 

 the wood-vessels ; but in older diseased plants the elements of the wood do 

 not become invaded with hyphae until the rotting has reached an advanced 

 stage. 



Hyphae of the kind described are always found in the diseased tissues of 

 affected plants; and if such plants are only recently attacked, these hyphae con- 

 stitute practically the whole of the mycelium present. This mycelium, as will be 

 seen from a subsequent section of this paper, was found to belong 1,0 a hitherto 

 undescribed species of Phytophthora. Of course in later stages of the disease 

 the dead tissues become invaded with saprophytic fungi and bacteria of 

 various kinds; and these add considerably to the difficulty of making a 



satisfactory diagnosis of the actual parasite in advanced cases of the disease. 



4g2 



