ON THE PERONOSPORiE. 



211 



Potato plants as hosts to nurse them. 4.— Be sure the seed 

 Potatoes are free from disease when planted, as a few diseased 

 plants will infect acres of Potatoes in a wet, warm season. 5.— 

 Chemical manures are preferable to other manures, being less 

 likely to contain mildew seeds. 6. — Potato crops may sometimes 

 be saved by pulling up the haulm directly the disease spots appear 

 on the leaves of any one plant. 



Want of space has prevented more than just alluding here 

 to the interesting experiments of Mr. Murray, who, by placing 

 glass slips covered with glycerine on the lee side of a field of 

 diseased potatoes, obtained numerous spores of Peronospora 

 Infesfa?is, demonstrated the important part the atmosphere has in 

 distributing the summer seeds of the disease. When scientific 

 witnesses speak of millions of spores being found in each diseased 

 plant, which may thus be wafted about in the air ; and when they 

 are of opinion that even birds and ground game may be the means 

 of carrying the infection from one place to another, we see the 

 impossibility of ever being able to root out the disease. Atten- 

 tion to the details of scientific cultivation, the choice of new and 

 strong varieties of tubers for seed, and the gradual restoration of a 

 stronger constitution to the Potato by this means, is the direction 

 in which we must look for future success. 



EXPLANATION OF PLATES XX., XXL, XXH.^ 



XXIII. , XXIY. 



PLATE XX. — Peronospora infest ans. 



Fig. 1. — ( X 150) Mycelium and branched conidiophore, taken from the 

 surface of a slice of diseased Potato which had been exposed 

 to damp air. c, Toung conidia. 



2. — (x 390) Fragment of a branched conidiophore, like the pre- 

 ceding, but older, having produced conidia, and showing 

 numerous partitions. 



3. — ( X 390) Pipe conidia. 



4. — (x 390) Conidia putting out germ tubes. 



5. — (x 390) Thin fragment taken by a vertical cutting from a 

 slice of Potato, the surface {s.s.) of which has been sown with 

 spores of P. infestans. Two germs have perforated the 

 partitions of the superficial cells of the slice ; one has entered 

 tlie intercellular meatus of the subjacent parenchyma, the 

 other has not yet quitted the cavity of the superficial cell. 



5) 



55 



5) 



