232 
THE PLANT WORLD. 
hollow centers of the starch grains. The light color of the starch 
is due to the transparency of the grains brought about by the 
medium of preservation. 
It is my purpose at a later date to discuss some features of the 
physiology of the germinating barley-corn. 
THE TEACHERS DEPARTMENT. 
Edited by Professor C. Stuart Gager. 
Are Potato Tubers Caused by a Fungus? —Various experi¬ 
ments have been carried on for the purpose of determining the 
conditions for the profitable cultivation of Solanum commersoni, 
a close relation to our common potato, a native of the eastern por¬ 
tions of South America. The great practical interest of this 
plant lies in the fact that it grows in marshy soil that is unsuited 
to other crops; but so far its successful cultivation with edible 
tubers has been limited to the grounds of Labergerie, near 
Vienna. It has been supposed that this species is the progenitor 
of the cultivated potato, but nothing definite has been determined 
on this point. 
In S', commersoni the tubers are small, and are formed very 
slowly at the ends of long stolons. From results incidental to 
some extended researches into the relation of endotropic fungi 
to the formation of tubers in various plants Noel Bernard* in¬ 
fers that these qualities were characteristic of the 5 \ tuberosum, 
when that plant was first introduced into Europe; and that it was 
only after the soil had become generally infected by the endo¬ 
tropic fungus peculiar to the potato that tuberization became 
earlier as well as more regular and abundant. 
It occurred to M. Jumelleif Is it not possible, by infecting 
artificially at the time the tubers are planted, to reach at a single 
stroke the point it had taken so long to reach in the case of N. 
* Bernard, Noel. Etudes sur la tuberisation. Revue General de Botanique, 
14: 5, 58, 101, 170, 139, 269. 38 figs. 3 pis. 1902. 
f Jumelle, Henri. De l’influence des Endophytes sur la tuberisation des 
Solanum. Rev. Gen. de Bot., 17: 49. Feb., 1905. 
