Dying of the Lower Leaves and " Black Root." 



Beyond this, as the plants go on toward maturity, some plants are 

 found in almost every large house which are affected and injured, 

 but not always killed outright by the gray mould. In these cases 

 the direct effect is found in the lower, older leaves. Some of these, 

 often only one or two on the same side of the plant, slowly rot off 

 at the base. The stem and fleshy raid-rib of the leaf rots out, the 

 green blade withers away, and along on the rotten part the gray, 

 dusty aiiould appears, which, if the leaves mat down close together, 

 may spread all over the leaf. By this rotting off of the leaf a black 

 spot is left on the side of the stem, and where several go off close 

 together the whole side of the stem, just at the surface of the soil, 

 looks black and rotten. It does not, however, in typical cases of 

 this sort, rot deep into the stem, but simply at the surface. This 

 loss of the lower leaves and slight decay of one side of the stem is 

 not without its effect upon the head and inner leaves of the plant. 

 No fungus or rotting appears in these, but the head does not fill up 

 properly and the inner leaves remain slender and straight, standing 

 out separate from one another in something of a rosette. This 

 trouble is well known to the growers and is called by them " Black 

 Root." In some houses it is quite abundant. Plants are affected 

 in all degrees and many are marketed which show the trouble to 

 some extent, but they are of poor quality, being imperfectly headed 

 and rendered unattractive in appearance by the black, decayed look 

 of the stem. The loss of the lower leaves is directly reaponsible 

 for this trouble and there can be no remedv save a handling of the 

 crop which will keep the outer leaves growing and prevent their 

 rotting off. This is accomplished by the best growers, in whose 

 houses the loss from this source is reduced to a minimum. Black 

 Root is especially abundant in crops where the outer leaves died off 

 in transplanting, thus checking the plants and giving the fungus 

 a foot-hold. The ability to carry the plants through this stage with- 

 out a setback is the chief requisite for preventing this disease. 



Rotting of the Stem of Mature Plants. 



In the report of the Massachusetts Experiment Station for 1891 

 Dr. Humphrey described a disease of greenhouse lettuce in part as 

 follows : '' The trouble ordinarily appears first upon the stem of the 



