S botanical gazette. [January, 



'cross-section. This line, according to Gerber, indicates the 

 • degree of tension produced by the pressure of the new cells 

 growing within the zone of cork cells. Now, the significant 

 tact in connection with this in the cork wing is, there is no 

 such tension from pressure of the growth within, because the 

 •constant breaking of tissue from the outside prevents it. The 

 -cells, which are arranged for this purpose, keep their rectan- 

 gular form. The plate cells of the fall growth, which form 

 a connected zone about the stem in Quercus and Acer and 

 in Liquidambar connect with the regular periderm of the 

 rest of the stem, have not this contrivance for stretching, and 

 it may be supposed are more easily broken by the pressure 

 within when the sudden and vigorous growth of spring be- 

 gins. On the other hand, it was found that in the majority 

 •of specimens the walls of the plate cells were decidedly 

 thicker than those of the summer cells, and in nearly all 

 cases both radial and tangential walls were bent and curved. 

 In the formation of the wings of Quercus and Acer and 

 others of a similar type, the first steps in the process are 

 easily explained on the score of purely physical causes. The 

 breaking of the tissues is the result of "the strain, greater 

 here than m other places, on the fresh vielding tissues. The 

 increased rapidity of growth following this breakage is 

 not unlike that caused by a wound external. Verv soon, 

 however, in Acer there is a change in the place of growth ; 

 that portion exposed by breakage to the more free action of 

 the air is soon built out, so that manv layers of cells occur 

 between the phellogen and the external portion. (See a in 

 ng. 3.) iNo^ reason suggests itself for the change in the 

 place ol rapid growing to the center of the wing, Except the 

 one which may be used when all others fail, namely, inher- 

 ited tendency in this species. With Quercus this change of 

 base in growth either does not occur or is much more gradual. 

 As to the question of possible or probable advantage to the 

 plant m these two examples, a few words on the function of 

 lenticels are necessarv. 



™iJrtf n ^ al th6y at " e hdd t0 be t0 the superficial periderm 

 rt£ tW« K° maUl are - t0 the epidermis. Notwithstanding 

 W, rt S , ™ tl & ratlons m ^e of these organs at different 



their ;^t e "a a ? Pea " S *? bG SOme q uestion in regard to 

 their exact mode of action in all cases where they occur 



Haberl andt* says that in c ase of green stems without per- 



^r^^ZF^F' ; ,r Ke,mtn5SS '" r:;:;; ^^^^enchte der k. Akad 



