[KIRSCH] ORIGIN AND DEVELOPMENT OF RESIN CANALS 83 
is very young, but this, according to our interpretation of the phenome- 
non, would not necessitate putting them in a separate class. 
MeNicoll (20, 409) states that the function of the “cavity paren- 
chyma ” in the ferns is to store water, but this was certainly not the case 
in the forms examined by us, the cells there being of the same nature as 
the wood parenchyma from which they arose. It may be in place to 
state that Russow did not interpret the “cavity parenchyma” to be 
structures of a thylosal nature, as both Chrysler (8, 204) and MeNicoll 
(20, 1) assert, but that he took them to be a portion of the phloem which, 
on account of the irregularity of its component cells, afforded cavities 
between them. Thus, “ Liickenparenchym, according to Russow, (28, 
101) meant parenchyma showing large intercellular spaces between 
the cells, and not cells filling a cavity, as the authors mentioned above. 
erroneously interpreted it. 
Finally, the general rules governing thyloses wherever and when- 
ever they appear may be stated to be as follows: 
1. There must be present living cells capable of growth. 
2. A diminution of pressure in the lumina on which these cells 
border and to which they have access. 
3. There may also be the possibility of an increase in the turgor 
of the living cells bordering a cell or canal lumen, and this would have 
the same effect as the second cause. 
In conclusion, I desire to express my sincere thanks to Professor 
D. P. Penhallow for the aid he rendered me in the carrying out of the 
present research, not only affording me the full use of the laboratory 
and of his private library, which latter proved of the greatest help, 
but also for his readiness to elucidate any difficulties which arose in the 
course of the work. I also wish to thank Professor Miss C. M. Derick 
for the continued interest she showed in the progress of the investiga- 
tion, and for her many helpful suggestions. To Mr. Edward Ardley 
of the Redpath Museum, I am greatly indebted for his kindness in 
collecting some of the material used in the course of the investigation. 
McGill University, April, 1909. 
