1840.] SENATE— No. 36. 59 



case ill which rust appears, is where the plant seems to be 

 excessively forced by high manuring and a peculiar state of the 

 weather. Where the growth of the plant is very luxuriant, 

 and there occurs a kind of weather common in July and 

 August, half rain and half sunshine, oftentimes the sun and 

 the rain alternately contending for possession and the heat 

 intense, vegetation then is forced to its utmost speed, and it 

 would seem as though the sap vessels were burst by repletion ; 

 and the exudation of the sap causes the rust which then ap- 

 pears upon the stalk. Against this there is no remedy known. 

 This same disease or accident is common with herds-grass or 

 Timothy, in time of drought, especially when the crop is thin 

 and the ground light and scantily manured. 



Mildew. — The second disease is blight or mildew, in which 

 the plant assumes a purple or bluish cast, resembling the mould 

 which collects in damp places in houses upon articles of furni- 



by the end of the week it was brought into fine tilth. Notwitlistanding the 

 whole week had been dry with a strong sun and a sevei-e east wind, yet 

 sucli was the progress in growth of the cabbages, that wlien seen again by 

 that gentlemen on the Saturday he could scarcely be persuaded they were 

 the same plants. During these operations, I had been making constant ex- 

 periments with glasses contrived for the purpose, to ascertain the quantity 

 of evaporation from the land, which I ibund to amount, on the fresh- 

 ploughed ground, to nine hundred and fifty pounds per hour on the surface 

 of a statute acre, while on the ground unbroken, though the glass stood 

 repeatedly for two hours at a time, there was not the least cloud upon it 

 which proved that no moisture then arose from the earth. The evaporation 

 from the ploughed land was found to decrease rapidly after the first and 

 second day, and ceased after five or six days, depending on the wind and 

 sun These experiments were carried on for many months. After July 

 the evaporation decreased, wliich proves that though the heat of the atmos- 

 phere be equal, the air is not so dense. The evaporation, after the most 

 abundant rains, was not advanced beyond what the earth afforded on being 

 fi-esh turned up. The rapid growth of my potatoes corresponded perfectly 

 with the previous experiments ; and their growth in dry weather visibly ex- 

 ceeded that of other crops where the earth was not stirred. The compo- 

 nent parts of the matter evaporated remain yet to be ascertained ; the 

 beneficial eflfects arising from it to vegetation cannot be doubted or denied • 

 but whether they proceed from one or more causes, is a question of much 

 curiosity and importance." — Curwen^s Hints, p. 274. 



