KEPOET OF THE BOTAXIST, 85 



weeds, aucl Peronospora effusa deserves a good word for confining its 

 attacks to tlie common j ig-weed (genus Chenopodinm). 



The wbite rnst disease of cabbages is due to a- very common fungus 

 of the order Pcroiwspoyecv, named Cysiopus candidus. It is especially 

 abundant early in the season on the well-known shepherd's purse and 

 other cruciferous weeds. Unlike the Fcrcnospora, this cystopus forms 

 its conidial spores beneath the epidermis, which, in conse«iuence, is dis- 

 teuded, forming whitish pustules. When seriously atiectcd the stems 

 and leaves of cabb;iges and caulitiowers become swollen and distorted, 

 and si)otted with white streaks and blotches as if bespattered with 

 whitewash. 



Clean culture, and the destruction of those weeds that support the 

 fungus in question, together with a proper alternation of crops, will no 

 doubt check its ravages. 



Dr. Maxime Cornu, in speaking of the mode of treatment for the dis- 

 eases caused by Peronosporecc * says, that when the entire plant is at- 

 tacked it should be got rid of at once; it is a hot-bed of infection. In- 

 fected leaves should be removed, so tliat the jjlant may not contaminate 

 itself or oth -r ])lants j this shiudd be done with precaution, in dry 

 weather, when there is neither wind nor dew. Destroy as far as ]>ossi- 

 ble all the seeds that may harbor the i)a!asite, and all weeds that uiay 

 su])port it. All ]>lants, or portiiuis of plants, wlutl'.er green or withered, 

 infected hx tho Perouaspora or its mycelium, sluuUd be removed; the 

 green portions, if left on the ground may, in dauip weather, produce 

 fresh spores : the withered portions may coutain resting spores, and 

 so become a source of danger. Thej' should be entirely destroyed, 

 either burnt or deeply buried. In no case should they be used for ma- 

 nure or as food for domestic animals, as is often done. 



Enough has been said to illustrate the importance of the study of 

 plant diseases due to parasitic fungi, and certain general principles in- 

 volved in combating them have been pointed out. I may add that this 

 subject has a wider interest than pertains to our "ileld and garden 

 crops." There are itiany fungi which are ])arasitic on ouf forest trees, 

 often productive of great injury, while others are no less injurious to 

 prepared timber. And, finally, the subject is one of vast importance to 

 the stock-rifiser, for there is no class of plants more often or seriously 

 attacked by fungi than the grasses — the chief forage plants of the coun- 

 try. It is not only that the quantity of the forage may be seriously 

 diminished, but the quality is often impaired with even more serious 

 results, for it is well known that someot the diseases which have caused 

 great losses to the cattlemen of the West are due to the presence of cer- 

 tain fungi in the grasses upon which the cattle feed. 



nONEY-DETV. 



iloney-dew is the term applied to a sticky, sweet-tasting, and nearly 

 colorless substance found upon the surface of the leaves of many plants 

 at certaiu seasons of the year, appearing like a smooth, uniform coating 

 of varnish over the surface, or in the form of yellowish, tenacious drops. 

 The nectar normally secreted by flowers or by special glands, and the 

 peculiar honey like substance found in connection with ergot in rye and 

 other grains, arc not here considered. 



Tlie honey dew in question may be jiroduced by plant-lice (Aphides), 

 by bark-lice (genus C'occ/), or by what appears to be a genuine secretion 

 of the leaf tissues themselves. 



• Coraptes Kendns, December, 1878. 



