RELATION OF SOME RUSTS TO THEIR HOSTS 1 9/ 
68, 70, 71, 72 plainly showed the lack of carbon dioxide in their lighter 
green leaves, which were dying back from the tip. 
The experiment was finished at the end of the twelfth day. There 
was no infection on FC-E 68, 70, 71, 72, which, although they showed 
indications of approaching death, were still alive. Not even greenish 
spots showed on the yellowing leaves such as often appear upon dying 
leaves in infected areas. FC-E 69 and 73 at this time had a number 
of open pustules and the plants themselves were in every particular 
as healthy as the checks, showing that the apparatus in these cases 
was defective and did not eliminate entirely all the carbon dioxide, 
or that the plants possessed a large enough amount of food at the 
beginning of the experiment to supply them. 
These two experiments show, as do those with light, that there is a 
relation between the development of the rust and the carbohydrate 
supply. 
Effect of Supplied Carbohydrates upon Development 
Since the preceding work indicated a relationship of the rust to the 
carbohydrate supply, further experiments were undertaken in order 
to study this relationship more thoroughly. To do this it is necessary 
to supply carbohydrates to the host which has been deprived of them 
as nearly as possible, since the experiments with light indicate that 
the host normally contains more or less carbohydrates in available 
form for the use of the rust. 
This work divides itself into two parts according to the manner of 
supplying the carbohydrates to the host. In the first case, carbohy- 
drates were supplied to the plant through the scutellum of the maize 
seedling and through the roots. Van Tieghem (1873) has shown that 
embryos can be developed upon starch. Brown and Morris (1890) 
have found that not only do excised embryos develop normally upon 
starch, but that they will also do so with sugar solutions, especially 
cane sugar, and that when both starch and sugar are present, the sugar 
is used up before the starch is attacked. 
A number of authors have investigated the ability of plants to take 
up carbohydrates through their roots. Maze and Perrier (1904) ob- 
tained a good growth of maize in i percent glucose and sucrose. 
Acton (1889) found that in this way acrolein, acrolein-ammonia, allyl 
alcohol, glucose, acetic aldehyde, ammonia, glycerine, laevulenic acid, 
calcium laevulinate, cane sugar, inulin, dextrins, glycogen, and extract 
