Biological Papers. 325 



lina, Ailanthus glandulosus, Acer eacoharinum (8), Acer negundo 

 (11), Tilia americana, Asimina triloba. Thirty-five twigs and fif- 

 teen species. 



Sixty- five of the twigs tested seemed to have some or all of 

 their lenticels open for respiration during the winter months, while 

 the other thirty-five did not have such provision. In about half of 

 the former cases, however, bubbles were seen from one-half or fewer 

 of the lenticels immersed, in some instances from but a small per- 

 centage of them. 



It was noticed that the two-year-old growth has generally more 

 open lenticels than the growth of the season, and that the three- 

 year-old growth has more than the two-year. Likewise, the older 

 lenticels appeared to have the freest passage for air. 



It was also rather remarkable that in the case of some species 

 tested, notably the papaw, some twigs gave decidedly positive and 

 others as decidedly negative tests. In several cases open and closed 

 lenticels of a species were marked, imbedded in paraffin, and sec- 

 tioned. No difference could be detected with the microscope. In 

 no case could an open intercellular passage be traced to the interior 

 of the stem, there seemingly being just beneath the filling tissue a 

 layer of cork without spaces such as histologists describe. , 



It appeared that generally the rank-growing shoots, such as the 

 water-sprouts from the base of the tree, had the lenticels more gen- 

 erally closed than did the smaller or more stunted shoots. 



In class D are only four species which were not placed also in 

 one of the other classes on account of their lenticels having been 

 in some instances found open; and of each of these four species 

 only one twig was tested. 



Lenticels were looked for on the roots of several species and 

 were found well developed on many but not all of them. Their 

 structure is quite similar to that of stem lenticels. I tested a few 

 with the pressure apparatus, with the following results : 



Class B. — Juglans nigra, Rhus glabra (2). 



Class C. — Rhus glabra (2). 



Class D. — Rhus glabra (2), Ailanthus glandulosus (2), Xan- 

 thoxylura amerioanum (2), Rosa sp., Sambucus canadensis. 



Summary. — Four with open lenticels, eight without. In several 

 instances root-lenticels were closed while the lenticels on the stems 

 of the same plant were open. 



