(Edema of the Tomato. 121 



elongated cells began appearing on the under side of the leaf veins and 

 mid-rib as well as on the under side of the petioles. In a few days 

 more the curling of the leaves was perceptible, and in about ten days 

 the leaves of nearly all the plants of these two lots were badly affected. 



Those of lots 1 and 2 represented only a very few of the cushions 

 on the leaf veins, and if the experiment had not been disturbed prob- 

 ably none would have appeared. During the period of about, two 

 weeks these plants were watered quite heavily twice by an attendant 

 who had not been apprised of the nature of the experiment. Not- 

 withstanding this, the difference in the plants resulting in the different 

 degrees of irrigation was remarkable. The result of this experiment 

 seems to be conclusive concerning the physiological nature of the 

 disease. 



Relation of tissue strength to the disease. An analysis of the laws 

 of plant growth in connection with a study of the tissue strength and 

 firmness of tjie tomato plants grown in the forcing house, as well as 

 their environment, shows that the operation of the same, forces which 

 have produced this trouble has also produced a structural condition of 

 the plant which renders it in the highest deofree susceptible. One of 

 the most striking things about the plants of the No. 18 variety is their 

 rank growth and the succulent condition of the stems, petioles, vein- 

 lets and mesophyll of the leaves. They are remarkable for their frail 

 and bulky nature. The young stems and petioles of a size up to 1 

 cm in diameter crush between the thumb and finger with very little 

 pressure. In this variety the stems, petioles and veinlets are very sub- 

 ject to the disease. In the Lorillard variety the stems have been very 

 little affected, the trouble occurring chiefly on the veinlets of the leaf. 

 A comparison of the tissue strength of these two varieties gives the 

 key to their different tendencies in this respect. A stem or petiole of 

 the Lorillard variety of the same stage of growth is in very strong 

 contrast with those of the No. 18. Grasped between the thumb and 

 finger there is a sense of great resistance to pressure, and when crushed 

 the tissue appears fibrous and little watery compared with the soft, 

 pulpy tissue of the No. 18. 



A microscopic examination of young stems of the same stage of 

 growth of these two varieties, presents the conditions upon which this 

 difference in firmness of tissue depends. Plate VIII, figures 17 and 18, 

 are from camera-lucida drawings of sections of stems from a No. 18 

 and Lorillard plant of the same stage of growth. In the Lorillard 

 plant considerable woody tissue has already made its appearance as is 

 shown in figure 18. The bast cells near the cortical parenchyma have 



16 



