1917] FAUST—RESIN SECRETION 445 
selected and dried in the middle of May, the time of maximum 
growth. This resin value was found after the ethereal oil had 
evaporated. By the osmic acid test it was found to contain no 
fatty oils. An analysis of B. terebinthacea made by Miss HERMA 
T. KreLLey (19) indicated 9.76 per cent resin, 8.96 per cent of 
which was removed by chloroform and 0.80 per cent by alcohol. 
In addition to this there were 5.70 per cent oils, 0.42 per cent 
_volatile oils, and 5.28 per cent of fixed oils. Lioyp (11) has cal- 
culated the percentage of resin for Parthenium argentatum, the 
guayule of the Mexican desert. His values are as follows: 
Per cent resin 
PU ek ea ee 2.46 
Wood growth of 1907............... a S96 
Cortex of ese WOO is ceed re oe an 
Growth Gt thon. or cee nde 2a 7.56 
New growth i 1909 with lekies eae a 2.70 
Rata AG Ce ke ey ee .. 10.80 
These values were obtained from irrigated plants. WHITTEL- 
SEY (25) secured from ro to 17 per cent of resin for the field plants 
of the same species. If the field records are taken, it is evident that 
by weight the resin content of B. sagittata is smaller than that of the 
related species, B. terebinthacea, or of Parthenium argentatum. 
Associated with B. sagittata in a parasitic way is a certain fly of 
the Typetenid group of the family Muscidae. A complete descrip- 
tion of this fly will appear in a separate paper now in preparation 
by the author. The fly is found in the receptacle of the maturing 
flower head, living there during the grub and pupal stages of its 
development. The grub is about 1.8 mm. in length by 0.15 mm. 
diameter, while the pupa averages 1.5 byo.15 mm. Usually there 
is only one individual to the receptacle, but certain receptacles have 
been observed by the writer in which 5 or 6 of the parasites 
lived. The grub is very insidious, ordinarily boring a labyrinthine 
course through the upper parts of the receptacle and into the 
bases of the maturing seeds. The result is a twofold injury to 
the seed: an actual destruction of the maturing seed and a stunt- 
ing of growth in the seed by intercepting the course of nutrition in 
the receptacle. 
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