I 889-] BOTANICAL GAZETTE. 



9 



iderm, when lenticels occur, they serve to hinder transpira- 

 tion, on stems with periderm they increase it. Zahlbruck- 

 ner 4 says, in winter they are permeable for air only in slight 

 degree, in spring they are fully open, that is, in a condition 

 to allow exchange of gases freely before the leaves have 

 reached^ their growth. Klebahn 5 says, a winter closing of 

 the lenticels does not exist, and that their permeability for 

 gases in certain plants is the same both in summer and win- 

 ter, in others, greater in the early part of summer. 



One glance at the anatomy of the wing of Quercus ma- 

 crocarpa and of Acer will suggest the possible connection 

 here. The lenticels are raised by the rapidly-growing wings 

 until they are separated entirely from the cells within the 

 phellogen layer which they are supposed to furnish with air. 

 Finally the outer cells break in regular lines along the cor- 

 ners of the stem, and during the first year, all along these 

 broken places, free communication between the phellogen 

 cells and the outer air is hindered only by the thin cellulose 

 walls of one or two layers of cells. We say cellulose ; we 

 have proven that these walls are in no case suberized ; they 

 may be slightly ligniiied, but even in this case would offer 

 less resistance to the interchange of gases than the suberized 

 tipper wall of the epidermis. 



We then have the furrow between the wings acting as a 

 continuous lenticel, in a less degree permeable, but still ren- 

 dering an interchange of gases possible. Now as winter ap- 

 proaches this furrow is closed, in every case, by a few layers 

 of real cork cells whose walls are suberized. In the spring 

 this zone of cells is broken, the same conditions are renewed 

 as in the preceding summer, as regards interchange of gases. 



The probability that these furrows serve the plant in this 

 way is increased in the case of Quercus by comparing its su- 

 perficial periderm with that of Quercus suber. In the latter, 

 the presence of the large and numerous lenticels, extending 

 from the phellogen layer nearly to the surface of the thick 

 periderm, and communicating there with the external air by 

 means of shallow cracks along the surface, shows conclus- 

 ively that the inner portions of the stem need to be in com- 

 munication with the outside air. These lenticels are entirely 

 wanting on the stems of Quercus macrocarpa. De Bary 6 

 states that lenticels lie in the furrows of the wings of 

 Acer camnestre. Euonvmus EuroDJtnis. Ulmus and Liauid- 



4 Abstract la Just's Jahresb. XII ( M) part 1, p. 265. 



6 H. Klebahn. Jenaische Zeitschrift fur Naturwissensehaft, 1S84, p. 588. 



•Anatomy of Phanerogams and Ferns, p. 56'2. 



