344 



to ascertain the exact life-liistory of this species and the best time at which to fight 

 it. You can donbtless rid your trees at this time of the year by severe pruning, but 

 the probabilities are that in the spring there will occur a time when the mites wan- 

 der from their old galls to the new growth in order to form new galls. If this time 

 can be ascertained, which can be done only npou the sx^ot, it will be comparativelj' 

 easy to destroy these creatures by spraying the trees with a dilute kerosene emul- 

 sion. I trust that you will follow this matter up and not fail to let me know the 

 results and to send me specimens from time to time. I have every reason to believe 

 that the galls are the winter form produced hy PJujtoptus pruni-crumeni, which pro- 

 duces in spring the little purse-like galls on the leaf. — [February 1, 1888.] 



Second letter. — Yon think the galls on the plum tree may be a winter form of 

 growth ; the trees were infested the same during the summer and the summer previous. 

 I never could make myself believe that knots on plums and cherries were of fungoid 

 origin, as I always supposed they were caused by insects, as knots in the forest and 

 other vegetable life are recognized to be, but scientists say fungi, and of course I was 

 compelled to say so too. I now send you another package containing the regular 

 black knot and the galls sent you last week so inseparablj' connected with them that 

 I think you will say they precede the black knot, and I am inclined to believe that 

 they are the first appearance of the same. You will notice at the base of some short 

 spurs the pustules show the black and pinhead like sections of the fully matured black 

 knot, and by looking the specimens all over you will find a growing similarity from 

 the smooth fresh gall to the matured gall sections of the hard black knot ; and it 

 would seem that the development of the younger galls was arrested by the close of 

 the growing season. I shall not be surprised if the branches that are covered with 

 these galls will another season be a perfect scab of the common plum knot. — [A. J. 

 Cay wood, Marlborough, N. Y., February 6, 1888. 



Second reply. — Yours of the 6th inst. with additional specimens came duly to 

 hand. The twigs are interesting and the abundance of the mite galls is surprising. 

 Their occurrence with the black knot is probably a simple coincidence as there is no 

 possibility that they can have any connection with the black-knot disease, which, 

 as is well known, is caused by a fungus (Plowrightia morhosa). It is barely possible 

 that the attacks of the mites by weakening the vitality of the twigs render them 

 more liable to the attacks of the fungus ; but beyond this no possible connection cau 

 be plausibly traced. — [February 8, 1888.] 



A Lac Insect on the Creosote Bush. 



* * * I also mail you a small package containing stems with exudations of the 

 creosote bush (Larrea mexicana) of which Dr. Loew says, ''the reddish-brown exudation 

 on the branches will yield a red coloring matter showing all the reactions of cochineal. 

 The alcoholic extract of the leaves on evaporation yields a greenish-brown residue of a 

 specific and somewhat disagreeable odor, more strongly perceptible on boiling the ex- 

 tract with water. This residue is only to a small extent soluble in water, and the so- 

 lution has an acid reaction. It yields a light yellow precipitate with acetate of lead. 

 The i)art of the alcoholic extract that is insoluble in water is easily soluable in alka- 

 lies. It also dissolves in nitric acid at a moderate heat, whereby oxidation takes 

 place. On addition of water, a yellow, brittle mass is precipitated." 



The Mexicans use an effusion of the leaves for bathing in, in rheumatic afi^'ections, 

 and as long as the disease is in its first stages, with remarkably good results. 



But apart from its medicinal i)roperties, I am led to believe that these exudations, 

 if properly examined, would give a splendid bright red coloring matter and a very 

 superior varnish resembling the celebrated Japan lacquer. Do not you think it worth 

 while to have the necessary chemical analysis made ? There are miles upon miles of 

 the bush growing here and far down into Mexico, audi should think that a man 

 could gather from 60 to 100 pounds of clear exudation matter in a working day of 

 ten hours. My supposition as to the qualification of producing a sux^erior varnish is 



