340 ANNUAL OF SCIENTIFIC DISCOVERT. 



The gum may be collected during the months of July, August, and Sep- 

 tember ; but the most farorable period for that purpose is in the latter part 

 of August, when it may be obtained in the greatest abundance and with 

 but little trouble. The quantity yielded by each tree I found to vary from 

 an ounce to three pounds ; but incisions in the bark not only greatly facili- 

 tated its exudation, but caused the tree to yield a much greater- amount. 

 As it is, a good hand would probably be able to collect from ten to twenty 

 pounds in a day. Were incisions resorted to, probably double the amount 

 might be obtained. 



Specimens of the gum hare been forwarded by Dr. Shumard to Mr. 

 Drew, and are described by the latter as strikingly similar to gum arabic, 

 not only as regards taste and appearance, but as to their mucilaginous 

 qualities. Mr. Drew states : " Upon diluting one ounce of this gum 

 in two ounces of cold water, I had a fine, glutinous paste, which I have 

 used in sealing envelopes and other packages. I have also caused it to be 

 mixed with starch in the application to linen, and, in both instances, have 

 no hesitation in saying that it is equal to the article of which it must soon 

 become a popular substitute." 



THE OIDIUM TUCKERI, OR GRAPE MALADY OF EUROPE. 



From a paper read before the Royal Institution of Great Britain, by M. 

 Brockedon, we obtain the following information respecting the singular 

 disease which has of late years proved so destructive to grapes of France 

 and other parts of Europe. 



It appears to have been first observed in England by an observant gar- 

 dener of Margate, whose name has been given to the fungus producing the 

 disease, viz., Oidium Tucker i. It is an egg-shaped fungus, one of an im- 

 mense family of this class of destroyers, but one not before known or 

 recognized ; and though it bears a close resemblance to those which are 

 found upon the potato, peach, cucumber, &c., yet it is distinguished from 

 all others by a microscopic observer, and has never yet been found upon 

 any other plant, and, when found upon the grape, has always been destruc- 

 tive. Its first appearance is like a whitish mildew, showing itself princi- 

 pally upon the young grape when about the size of a pea. When the 

 spore of this fungus has settled on the young berry, it enlarges and ra- 

 diates irregularly in fine filaments, which often cover the whole surface, 

 extending with great rapidity. These fix themselves by imperceptible 

 attachments, which do not appear to penetrate the cuticle ; numerous 

 branches from the mycelium are unfruitful ; others are jointed, and rise 

 vertically like the pile of velvet ; the upper joint enlarges, rounds itself 

 into an elliptical form, ripens, separates, and is carried off with the slight- 

 est motion of the air, to find another grape upon which it can be devel- 

 oped. Warmth and moisture favor its rapid fructification ; a succession of 

 spores rise from the same branch ; and often two, three, or four ripen and 

 disperse almost at the same time. Its effect upon the grape is to exhaust 



