140 
IOWA ACADEMY OF SCIENCES. 
die. Behrens has recently studied hops. According to him 
the formation of lupulin glands begin after complete develop- 
ment of the bracts, the ethereal oil is secreted between the cuti- 
cle and the cuticularized membrane. He further remarks that 
the quantity of lupulin grains is dependent upon fertilization. 
These glands serve as a protection from animals, and also that 
the only possible way of recognizing ripe hops is to find the 
lupulin grains filled with this lupulin. 
It is gradually soluble by water, and instantly so by alco- 
hol and ether. 
The covering of the calyx has on it many glandular hairs 
which secrete the resin and oil. 
Examined under the microscope it appears to be made up of 
minute transparent grains of brown resin agglutinated with 
short hairs of the plant. 
EXPLANATION OF PLATE. 
In Pig. I is shown one of the fruits of the Ptelea trifoUata. The glands 
appear as minute dots over the surface of the fruit, being more numerous 
directly over the seed. 
Fig. II is a cross-section of one of the glands of the fruit of Ptelea tri- 
foliata, showing the resin and oil globules. The fragments of some of the 
cells may be seen around the edge of the gland. The gland occurs just 
beneath the epidermis. 
Fig. Ill is a surface view of one of the glands of the fruit of Ptelea tri- 
foliata. The resin and oil globules are shown surrounded by the regular 
cell structure. 
Fig. IV is a cross-section of one of the glandular hairs on the fruit of 
true hops, Htimulus lupulus. 
Fig. V is a view from the top of one of the glandular hairs which occurs 
on the hemp, Cannabis sativa. 
Fig. VI is lateral surface view of one of the glandular hairs which, 
occurs on the hemp. Cannabis sativa. 
