VIII 
Journal of Agricultural Research 
Vol. VII 
Page 
Plate 3. A to I, L, M.—Drawings and diagrams representing the distribution 
of precipitate resulting from the fumes of 40 per cent nicotine sulphate and 
phosphomolybdic acid. A.—Transverse-longitudinal section of a trachea of 
an aphid, showing the precipitate inside the trachea and in fat cells near by. 
B.—Cross section of a portion of an aphid just molting, showing the precipi¬ 
tate on the outer surfaces of the old and the new integuments and between 
them, but none in the fat cells. C. : —Combination drawing from six con¬ 
secutive sections through thoracic ganglion of an aphid, showing the pre¬ 
cipitate in three tracheal branches in the cortical layer and in the inner 
layer of a ganglion. D.—Diagram of the dorsal tracheal system of an aphid, 
showing the dorsal trunk and dorsal arch. E.—Diagram of the ventral 
tracheal system of an aphid, showing the anterior ventral arch, posterior 
ventral arch, and the ventral trunk. F.—Combination drawing from five 
consecutive sections through the thorax of an aphid, showing the precipi¬ 
tate on the outer surface of the integument, in the tracheae, and in the sub- 
esophageal ganglion. G.—Portion of cross section of an optic lobe of an 
aphid, showing the precipitate inside and outside a tracheal branch. 
H. —Cross section of the brain and optic lobes of an aphid, showing the pre¬ 
cipitate in the tracheal branch and in the cortical layer of the brain. 
I. —Cross section of two ovaries of an aphid, showing the tracheal branch 
containing precipitate passing between them. L.—Cross section of two 
tracheae and a fat cell of a house fly, showing the precipitate in the tracheae 
and in the fat cell outside its nucleus. M.—Longitudinal section through 
a spiracle and its connecting trachea of a house fly! showing the precipitate 
in the neck of the spiracle and along the tracheal wall. J and K.—Cross 
sections of the small tracheae, showing the precipitate in newly formed 
tracheal walls resulting from the union of pure nicotine and phosphomolyb¬ 
dic acid. N and Q.—Cross sections, showing how well Camoy’s fluid passes 
through hard chitin, as indicated by remaining crystals of mercuric chlorid. 
O.—Cross section of a medium-sized trachea of a lesser wax-moth larva, 
showing that pure nicotine did not pass into an older tracheal wall under * 
the same conditions as stated for figure K. P.—Cross section of portion of 
the integument of an aphid, showing that pure nicotine did not pass into 
chitin under same conditions as stated for figures J, K, and 0 . 122 
Life History of Habrocytus medicaginis, a Recently Described Para¬ 
site of the Chalcis Fly in Alfalfa Seed 
Plate 4. Habrocytus medicaginis: A.—Adult. B.—Cages for rearing parasite 
larvae. C.—Larva. D.—Larva destroying its host larva. E.—Pupa. 154 
Daily Transpiration during the Normal Growth Period and its Corre¬ 
lation with the Weather 
Plate 5. A.—Six pots of alfalfa used in transpiration measurements. B.—Six 
pots of com used in transpiration studies.. 213 
Plate 6 . The type of spring balance and lifting device used in the transpira¬ 
tion measurements. 212 
Spongospora subterranea and Phoma tuberosa on the Irish Potato 
PLATE A. Spongospora subterranea and Phoma tuberosa on Solanum tuberosum: 
1-5.— Spongospora subterranea as found on different varieties of the Irish 
potato. 6, 7.—Stages in the development of dryrot caused by Phoma 
tuberosa . 254 
