274 
Mac Dougal, 
in lengtli showing a diameter of as great as 1 cm at the junction with 
the crown. The tissues of the thickened organs were turgid and crisp 
resembling radishes in consistency and taste. Ihe amount of tlie peculiar 
volatile oils present was noticeably greater than in normal plants being 
distinctly discernible by smell and giving a strong taste (Fig. 12). 
The internal structure of the roots sliowed correlated divergences. 
The central cylinder becomes greatly enlarged by secondary thickening 
in the terrestrial organs and a corresponding increase takes place in 
the cortex. In addition to the greater number and size of the various 
elements concerned the terrestrial organs are crammed with starch 
whicli appears to be wholly lacking from aqnatic organs, thus showing 
that the roots have been altered from a form suitable to fixation only 
to a structure adapted for receiving quantities of sugars and Converting 
this substance into starches which are stored in all of the parenchymatous 
elements. The embryonic tissues remain active in the periphery of the 
central cylinder and the phelloderm was visible in both cases although 
its growth did not keep pace with the enlargement of the terrestrial 
roots in all instances some of these organs having undergone Splitting. 
The terrestrial cultivation of these plants was continued. The plants of 
the original lot set out in 1902, produced aerial stems in 1905 which 
had internodes 3 to 20 mm long, by September of that year. The 
leaves and stems underwent an autumnal death however. Cuttings put 
out in 1904, showed clusters of thickened roots in 1905 which were 
much smaller than those set out in 1902 and material was preserved 
for a comparative examination, which might detect any developmental 
changes with continued cultivation. 
It was not possible to take up this point until the summer of 
1912 when the structure of the two lots of material was compared. 
The chief advance or change to the older condition of the thickened roots 
consisted in the more pronounced development of sclerenchymatous tliicke- 
nings of the cortical cells. The greatest number of elements modified in 
this manner lie immediately internal to the phellogen, but numbers of 
cells with such thickened walls are scattered throughout the cortex. The 
central cylinders of the older roots also showed an exaggerated deve¬ 
lopment. 
The observations the results of which are described in the pre- 
ceding pages extended over many years and included a consideration 
of the behavior of the plants under widely dissimilar climatic and other 
conditions. It is believed that very nearly the possible ränge of behavior 
has been noted. After these cultural experiments were well under way 
