460 BOTANICAL GAZETTE [DECEMBER 
i. Both passages opposite the bundle....... Solidago limonifolia 
ii. Medullary passage opposite the bundle, but cortical passage 
in the interstices between bundles . . Balsamorrhiza sagittata 
b) One medullary and several cortical passages 
Serratula centauroides 
2. A group of medullary passages for each group of cortical ones 
Gren Comibaet oo ie be ae arduus pycnocephalus 
b) Groups in curved series................... Helianthus tuberosus 
II. Passages wholly without bundle strands 
A. Passages external; not walled in on inner side by endodermis or 
ON ais gis i ke PG As Vane Solidago odora 
B. Wall of passages partially formed by endodermis or pericycle 
1. Passages single, not in grou 
a) One passage in middle at outer margin of each main leaf 
ORG a ee ee eee ee Senecio vulgaris 
b) One passage in middle of outer margin of each main leaf 
trace; in addition one passage for each single bundle in 
A 
MT A AP a a i ee he ster sp. 
c) One passage on each side close to phloem of each main 
eeied WER ee ee ee Tagetes patula 
2. Passages in 
a) Three to ns passages opposite outer margin of phloem and 
of minin Dene oie ie Silybum marianum 
Physiology of resin secretion 
Numerous theories have been proposed to explain the origin of 
resin and the methods of resin secretion. Among the more impor- 
tant sources conceived as a basis for resin formation may be named 
the following: starch, cellulose, tannic acid, phloroglucin, a hypo- 
thetical glucoside, terpene, and even chlorophyll. As diversified as 
are these substances, there may be at least superficial reasons for 
relating resin to any one of them. However, only a deeper analysis 
of the problem, following out a particular coincidence of resin and 
one of these materials, will show whether the relationship is a genetic 
one or not. Evidence is here presented showing certain relation- 
ships of the resin secreted by B. sagittata. 
The resin of this plant appears as a viscous exudation, especially 
from newly dug roots. It is a light lemon color in smaller quan- 
tities, but in larger amounts (ether extraction) it appears a golden 
yellow. It contains a small amount of essential oil, but gives no 
