ON THE PERONOSPOR^. 208 



Besides being so destructive to plants used as food, this fungus 

 causes equal havoc amongst flowers of certain descriptions. Thus, 

 in the Gardener's Chronicle for 1862, Berkeley describes the effect 

 of P. sparsa on roses in the following way : — '* A quantity of 

 potted rose-plants in a cool house suddenly began to fail, and in 

 a short time every plant died. Irregular pale brownish spots ap- 

 peared on the upper surface of the leaves, which soon withered 

 and shrivelled up, and ultimately the whole plant was sacrificed. 

 The zoospores were observed moving about with great rapidity by 

 means of lash-like threads." And again, in April, 1863, he des- 

 cribes the fungus as attacking between 3,000 and 4,000 roses in 

 one garden. As the fungus burrows amongst the tissues of the 

 leaves, it cannot be destroyed except by destroying the leaf. 



The red corn-poppy is attacked by P. arborescens^ the wood 

 anemone by P. pygmcea, the veronica by P. grisea, the sandwort 

 by P. arenaricB, the ranunculus by P. ficaricB^ the Rhinanthus by 

 P. dejisa, the lamium by P. lamii^ and so forth. 



There are now about forty-five described species of Peronospora^ 

 and when we consider that each of these probably possesses the triple 

 mode of reproduction already described, the conclusion is irresis- 

 tibly forced upon us, that this genus of fungus is almost unparallelled 

 in the amount of damage it is capable of inflicting on the vege- 

 table kingdom. 



P. Infestans, Potato Peronospora. 



Threads of mycelium slender, always destitute of suckers ; 

 pestile threads thin, gradually attenuated upwards, with one to five 

 branches, one or more inflated vesicles near the apices of the 

 branches ; branches either simple or with short branchlets ; 

 acrospores ellipsoid or ovoid ; apex furnished with a prominent 

 papilla. — (Cooke). 



Besides producing the well-known Potato disease, this species 

 also attacks the Tomato, the leaves of which become greatly 

 spotted, the stems partially blackened, and in some cases the 

 young green fruit is rotted, the fungus penetrating the rind of the 

 fruit direct from the outside. The Gardenet^s Chronicle contains 

 the record of a serious outbreak of this disease amongst the 

 Tomatoes at Bath, in the year 1852. 



