294 BOTANICAL GAZETTE [ NOVEMBER 
time to time, and water was added as it was lost by evapora- 
tion. Knowing the gram-molecular, and hence the percentage, 
strength of these stock solutions, any strength of Knop’s solu- 
tion may readily be made up from them; and solutions so made 
up are much more accurate in their proportions than those made 
in the ordinary way; for in dealing with salts such as mag- 
nesium sulfate and calcium nitrate the amount of water con- 
tained in the compound as taken from the laboratory bottle is 
always an uncertain quantity. All troubles arising from erystal- 
line and amorphous, as well as deliquescing, salts may thus be 
readily avoided. The exact amount of ferric salts in my solt- 
tion was not determined, The transfers of material from an old 
culture to a new were made, after a pure culture was obtained, 
by means of a needle. This was first heated in a flame and 
then cooled by plunging in the new culture fluid. Bits of steel 
always scaled off in this operation, and these furnished sufficient 
iron for the plants, 
In making up culture media from the stock solutions . 
constituent salts, it is necessary to dilute as far as possible 
before bringing the K, HPO, and Ca(NO,), together. As was 
remarked by Klebs, this avoids, in a great measure, the sepat- 
ating out of quantities of CaHPO,. This method is not com- 
pletely satisfactory, however, and it would be better 5° to | 
modify the proportions as to avoid the white precipitate entirely: 
I have planned to do this in future work. A solution made up 
of the quantities of the salts given by Knop dissolved ar 
parts of water is, of course, a 7 per cent. solution (since — 
iron is of such small amount it may be disregarded). aoe 
further diluted to 1 per cent., 1.5 per cent., and 2 pe sacs 
growing the stock material. : 
of the 
Investigation. la 
At the outset it was found that if material in the pale! 
form were transferred trom a 1 per cent., 1.5 pet crs i ae 
cent. solution where it had been growing for some me 
solution of less than 0.5 per cent., the plants responded : 
