604. ON PLANT GROWTH HORMONES 
are being synthesised in my laboratory. If our working hypothesis is in 
the main correct, the problem consists further chiefly in determining the 
way in which the ultimate residue of Cy is attached to the glutaric acid and 
to the corresponding cyclopentene ring. Perhaps we can obtain further 
insight into the constitution of auxin by the syntheses of octyl glutaric acids 
and dibutyl glutaric acids which are in progress ; in this connection we are 
especially concerned with isoprene as a possible unit. We shall of course 
also utilise X-ray analyses, and we sincerely hope that it will not be necessary 
to synthesise and resolve all the 1,200 substituted glutaric acids containing 
13 carbon atoms ! 
Although it was of course self-evident that we should first try to isolate 
the vegetable growth substance from the most favourable source, we were 
conscious from the very beginning that its isolation from vegetable sources 
should next be attempted. Our whole experience indicated that the reac- 
Ci, 
Cth, Cth Oh CCC - CHG Ne=ctt cy ct ctt. 
“4 & On * On OF by 
| ee. 
Oh Ch, 
Ch-Ch-CH-CH-C hCG ZD, 
pn hepyl.odenio Ce 
Ch CH 
CH Cthy Ch; Cir Oh” Yc=0 
#-n-heptyl cyclohexanone C-Ch 
Cy Oh Ct Cie Cth Ch Ch HCE 
-2-R Cadi 20 £ 
ih hol A a 
Fic. 7. 
tion of Went is a strictly specific test, and it seemed likely that the active 
substances from various sources were identical or very closely related. 
But recently such predictions require, more than ever, experimental proof, 
for in the case of the follicular hormone (cestrine) it has been found that the 
“lock * can be opened not only by the classical ‘ key,’ but also, more or less 
easily, by rough copies, or even by skeleton keys. 
My collaborator, Kostermans, has undertaken the difficult task of isolating 
the vegetable growth substance from yeast, which requires a concentration 
of about 500,000-fold. Miss Erxleben has already succeeded within the last 
few months in obtaining active crystalline material from other vegetable 
sources, first from maize germ oil and then from malt. Both these materials 
are very closely related to the coleoptiles of oats, in which the growth 
substance was first discovered. Although specially favourable samples were 
used, the maize oil required a 300,000-fold concentration, malt one of 
100,000-fold ; the procedure employed was essentially that worked out 
for urine. Both from maize oil and from malt two active crystalline sub- 
stances were obtained. The first was found, by means of its melting point, 
mixed melting point, analyses, and physiological action, to be identical with 
auxin isolated from urine. The second crystalline substance melted 13° 
