Potato CultuM. 



At first this mould forms webby, 

 creeping filaments, known in botanical 

 language as mycelium. These root- 

 like fibres then branch out, sending 

 out straight or decumbent articulated 

 steins. These bead-like joints fill up 

 successively with seeds or spores, which 

 are discharged at the proper time to 

 multiply the species. 



Under favorable conditions of 

 warmth and moisture, the mycelium 

 spreads very rapidly. Spores are 

 soon formed and matured, to be car- 

 ried to plants not yet infected. Rains 

 also wash the seminal dust down the 

 plant, causing it to fasten and grow 

 on the vine near the ground. The 

 roots of the parasite penetrate and 

 split up the stalk even to the medul- 

 lary canal. 



These roots exude a poisonous sub- 

 stance, which is carried by the elabo- 

 rated descending sap down to the 

 tubers, and as the largest tubers re- 

 quire the largest amount of elaborated 

 sap for their development, they will, 

 consequently, receive the greatest 

 quantity of the vitiating principle, and 

 will, on digging, be found a mass of 

 rottenness, when the smaller ones are 

 often but slightly affected. The Bo- 

 trytis infestans can not gain a lodg- 

 ment on vines that are truly healthy 

 and vigorous, high authority .to the 

 contrary notwithstanding. 



Healthy varieties, growing in a 

 sheltered situation on dry, new soil, to 

 which no nitrogenous manures have 

 been applied, can not be infected, 

 though brushed with other vines cov- 

 ered with the fungus. Different varie- 

 ties, and sometimes different members 

 of the same variety, are not always 

 alike affected by the disease, though 

 growing in the same hill. 



As will be noticed, the potato 

 disease is rather an effect than a cause, 

 and appears to have been designed 

 to prevent members enfeebled by ac- 

 cident or otherwise from propagating 



their species by putting such members 

 out of existence. Ozone, supposed 

 to be a peculiar form of oxygen, is 

 exhaled from every part of the green 

 surface of plants in health, and effec- 

 tually repels the attacks of mildew; 

 but it is found that when the atmo- 

 sphere is very dry, or, on the other hand, 

 very humid, plants cease to evolve 

 ozone, and are therefore unprotected. 

 Winds from the ocean are strongly 

 ozonic, and it is ascertained that plants 

 growing on soil to which salt has 

 been applied evolve more ozone than 

 others. Hence the benefit derived 

 from the use of salt on potato lands. 



The " Black knot," another species 

 of fungus that attacks the branches of 

 the plum and Morello cherry, operates 

 very similarly to the potato mildew. 

 The roots of the parasite penetrate 

 and split up the cellular tissue of the 

 branch on which it fastens, and if the 

 limb be not promptly amputated, the 

 descending sap carries the deleterious 

 principle through the whole system, 

 and the following year the disease ap- 

 pears in a greatly aggravated form in 

 every part of the whole tree. The 

 remedy in this case is prompt ampu- 

 tation of the part diseased on its first 

 appearance, and a judicious applica- 

 tion of salt to the soil. 



Common salt, to a certain extent, is 

 as beneficial to some plants as to ani- 

 mals ; and every intelligent farmer 

 knows that if salt be withheld from 

 the bovine genus for any considerable 

 length of time, the general health 

 droops and parasites are sure to 

 abound. The object of nature in 

 bringing into existence the large family 

 of mildews, each member of which 

 is a perfect plant in its way, and as ca- 

 pable of performing its functions as 

 the oak of the forest, was undoubted- 

 ly to prevent propagation from sickly 

 stock, and by the decomposition of 

 feeble plants to make room and enrich 

 the soil for the better development of 



