CHAP. IV.] WORK ON THE POTATO DISEASE. 29 



ment had not previously been chronicled. The disease was at 

 first considered a totally new malady, but Mr. Smee found, on 

 inquiry, that in Germany, in 1830, Martius wrote on the subject, 

 and that he attributed its effect to a fungus. Berkeley, the great 

 fungologist who, though differing in opinion from Mr. Smee, 

 always carried on the controversy in the most courteous 

 manner, and whom my father held in great respect and esteem 

 considered the fungus called the Botrytis to be the cause. 

 My father became interested in the subject, and began making 

 his own researches. He concluded that the first cause of the 

 disease was occasioned by an aphis which punctured the leaf, 

 sucked the sap, and destroyed the relation between the leaf and 

 the root, thus causing the leaf or some other part of the plant to 

 become gangrenous, and die. After the attack of the aphis, fungi 

 grew, which " growth," he writes, " is probably in many cases 

 materially assisted by the prior attack of the aphis." The results 

 of Mr. Smee's inquiries and researches on aphides, and their 

 relation to the potato and other plants, became so numerous, that 

 he was led, in 1846, into embodying his views on the subject in a 

 treatise containing 170 pages, which is well known by the title 

 of the * Potato Plant, its Uses and Properties, together with the 

 Cause of the Present Malady/ * In this book, which is dedicated 

 to the late Prince Consort, the properties and growth of the 

 potato plant are set forth, as is also its individuality, and the 

 chemistry and use of that plant, &c. ; its gangrene, or present 

 disease, and the chemistry of the disease; the relation of the 

 disease to internal and external causes ; the effect of temperature, 

 light, electricity, upon the disease; the relation of the disease 

 to soils and manures, to fungi; the relations of gangrene to 

 animal parasites. The various aphides are then described. The 

 insect that attacked the potato plant he considered to be an aphis, 

 which, when fully grown, is about a tenth of an inch long, and 

 its colour, either white, olive-green, brown, or inclined to red. 

 This aphis, the destroyer of the potato, he found was identically 

 the same which had been previously known to infest the turnip, 

 and which is called by Curtis on that account the Aphis 

 rapae. On the great confusion attending such a nomenclature, 

 Mr. Smee determined, for the sake of perspicuity, to call it 

 the Aphis vastator, or destroyer of our best provisions: for 

 the Aphis vastator destroys, in a similar manner as it does the 



* This book is still in print, and is published by Messrs. Longman and Co., 

 Paternoster How. 



