639 



of the stem, it will be injured in the same manner, but as both the 

 structure and function of the tuber, differ from that of the remainder 

 of the stem, some peculiarities will be observed. 



The starch which fills and distends the cellules of the tuber, has 

 been aptly compared with the fat of animals, and as it is sufficiently 

 evident that it is deposited as a fund of nourishment to the young 

 parts of plants, it performs precisely the same function in their eco- 

 nomy. But the fat of the animal, or the starch of the plant, is only 

 deposited when there is an excess of nutriment in the system ; and 

 it is to be expected that when there is a diminution of v itality, a dis- 

 ease of the digestive and respiratory organs and functions of the 

 plant, that this deposit of nutritious matter will also be deficient or 

 imperfectly developed. Now from the observations I have been able 

 to make, I come to the conclusion that the starch granules are either 

 deficient in number or bulk. On placing a slice of the diseased 

 potato under the microscope, many cells are seen perfectly empty or 

 containing only a few small granules, while in other cells they are 

 more numerous but still of small size. Now as the cellular tissue is 

 fully developed while the starch granules are deficient, their place is 

 supplied with a watery juice, which renders the tissue more prone to 

 decay. The decay as I have mentioned above commences in the cel- 

 lular tissue, and spreads along the walls of the cells, rendering them 

 brovvn and opaque. 



I find that this paper has already grown to a greater length 

 than I had at first intended. I could have wished to have entered 

 more fully on the general conditions necessary to the healthy per- 

 formance of the functions of a plant, the influence of atmospheric 

 changes and other analogous subjects, but other avocations and want 

 of time have prevented the fulfilment of my primary intention. I 

 shall therefore content myself with suggesting a remedy for the 

 disease in future crops. As there would appear to be defective vitality 

 accompanied by growth of fungi in this disease, I would suggest the 

 use of stimulating manures, such as common salt, or the chloride of 

 potassium, or even any other alkaline salts, taking care of course to 

 avoid too great a quantity, which would prove injurious to the plant. 



P. B. Ayres. 

 12, Howland St., Fitzroy Square. 



