274 ^^**^ Dougal, 



in length showing a diameter of as great as I cm at the junction with 

 the crown. The tissues of the thickened organs were turgid and crisp 

 resembling radishes in consistency and taste. The amount of the 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 showed correlated divergences. 

 The central cyhnder 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 

 which appears to be wholly lacking from aquatic 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 

 tlie original lot set out in J 902, 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 thicke- 

 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 range of behavior 

 has been noted. After these cultural experiments were welt under way 



