1889-] BOTANICAL GAZETTE. 43 



feature. Krabbe criticises these views, and insists that an 

 attempted explanation of the cause of fall wood should include 

 all the characteristics. The reviewer favors the opinion of 

 Wieler. 



These few statements contain, perhaps, the principal re- 

 sults hitherto attained in this direction. If it could be proven 

 that in the majority of instances the time of change from 

 summer to fall growth of wood does not correspond exactly 

 with that of the change in the cork tissue, the question would 

 then arise as to the cause of the latter. It is certainly very 

 significant that the only constant feature, viz. : shortened 

 radial diameter of cells, is common to both, and furthermore, 

 that the walls of the fall cork cells are often thicker than 

 those of the summer growth, which is so frequently true of 

 the fall cells of wood. 



On the other hand, if it could be proven that the time of 

 this change does correspond, there would be strong reason 

 for supposing the cause to be the same. This would invali- 

 date the theory of rind pressure, and add much in favor of 

 the opinion that the question is solved whenever the cause of 

 the shortening of the radial diameter is discovered. 



Owing to the difficulty of access to the living specimens at 

 proper times for experimenting but little could be done in that 

 direction. It is, therefore, scarcely proper to speak, in con- 

 clusion, of definite results. Various facts in regard to the 

 anatomy of these growths have suggested certain inferences, 

 some of which are of such a nature as to be easily proven or 

 disproven. The most important ol these are : 



I. Young stems, which are entirely encircled by cork 

 wings, were found to lack other means of communication with 

 the outside air. The anatomy of the wing in these cases is 

 such as to enable it to supply this deficiency and to act as 



• lenticels. 



II. The wings of the horizontal branches of Liquidambar, 

 covering as they do only part of the circumference, perform in 

 part the same function, at the same time they increase the sur- 

 face sufficiently to allow the growth within, while the remain- 

 ing part of the stem's surface retains the character and office of 

 the early periderm. 



III. In Euonymus, the symmetry of the stem is preserved, 

 the surface is enlarged by the wing, while all the remaining 

 surface of the stem plays the part of assimilation. 



IV. The characteristics of fall cork are exactly those of 



fall wood, the tracheal element alone excepted. Could it be 



