DISEASES OF PLANTS CAUSED BY PERONOSPOILE. 
93 
These observations cannot be applied to P. gangliiformis. 
2°. When the entire plant is attacked by the disease, it should be 
got rid of at once ; it is a hotbed of infection ; it is generally more 
elongated, paler, and more weakly than others. 
3°. The infected leaves should be removed , so that the plant may 
not contaminate itself or other plants ; this should be done 
with precaution, in dry weather, when there is neither wind nor 
dew. 
4°. Destroy without exception , as far as possible, all the seeds 
which may harbour the parasite ; in the case of P. gangliiformis , 
take away the composite plants, such as Circium arvense ; it is 
necessary to watch attentively chicory , artichokes, &c. ; consider 
them as a hotbed of infection, and, if necessary, give up their 
cultivation. 
5°* All plants , or portions of plants , whether green or withered, 
infected by the Peronospora or its mycelium, should be removed; 
the green portions left on the ground may, in damp weather, pro- 
duce fresh spores ; the withered portions may contain resting 
spores, and so become a source of danger. 
6°. They should be plunged at once into a solution which destroys 
the parasite (chlorate of lime, sulphate of potassium, etc.) ; other- 
wise the Peronospora may be spread. 
7°. They should be entirely destroyed , either burnt or deeply 
buried. In no case should they be used as manure or as food for 
domestic animals, as is often done ; the resting spores (oospores) 
do not lose their vitality or their hurtful properties. 
By following these instructions, which are general, and are easily 
applied to a large number of vegetable parasites, it will be possible 
both to neutralize the centres of infection and to prevent them 
spreading. The more valuable the crop, the more care should be 
given to their application. 
B. Mode of protecting the plant from the spores, and killing the 
parts attacked. 
In this case the peculiarities of the plant have to be considered. 
We will take the lettuces as an example ; many facts, however, 
applicable to them are general, and not restricted to them. 
it is known that this problem has reference to early crops only ; 
these are produced under the following special conditions : — 
The plant is — 1°, annual, and comes from seed ; 2°, it is pricked 
out ; 3°, it is cultivated under frames during winter and spring ; 
4°, it is planted in rich earth ; 5°, the crop is of short duration. 
1°. In sowing the seeds, rubbish should be removed, which might 
contain resting spores; the seeds should be carefully picked, or, 
better still, taken from healthy plants. 
2°. Pricking out. Healthy seedlings only should be used. leaves 
bearing the parasite generally perish later on, as I have seen in a 
great number of crops attacked by various parasites ( Uredo, JEci- 
aium, Puccinia, Stigmatea, Dothidea, Cystopus, Peronospora, and 
among them, P. gangliiformis. This does not apply entirely to 
