4° 



botanical gazette. [ February 





conclusions concerning the other species where corky pro- 

 jections occur, but which assume other forms than wings. 

 The so-called warty excrescences on the stem of E. verruco- 

 sus, examined after they were fully developed, showed no 

 difference between these and the ordinary cork formation, 

 and no traces of lenticels from which they are said to arise. 

 One species, E. Americanus, usually shows very few traces 

 of corky growth on its young twigs, and never, so far as I 

 can learn, produces the wing form. Some young stems 

 were found, however, with a distinct line of corky growth so 

 small as almost to require the lens to render it visible. This 

 line was neither along the corners, as in Europrcus, nor ex- 

 actly between them, as in alatus, but ran clost along the 

 side of each corner. This suggests very strongly the idea 

 of transition stages. The great variety in the matter of per- 

 iderm formation within this genus suggests a fertile field for 

 farther examination. 



It is quite possible that undue importance has been at- 

 tached to the fact of the difference betw r een the fall and sum- 

 mer growth of cells, and that the walls of the few layers of 

 plate cells are always suberized, while those of the summer's 

 growth for the most part show little traces of suberin. The 

 regularity with which this occurs, and the complete encir- 

 cling of the stem by one or more layers of suberized cells 

 during the winter, seem almost conclusive evidence that this 

 is to protect the stem during its period of winter rest, and 

 indicates also the demand for a greater supply of air in sum- 

 mer than in winter. This regularity, together with the tact 

 that in all cases studied, except the one previously men- 

 tioned, the number of the year's rings of cork agreed with 

 that of the woody tissues suggested that the immediate cause 

 producing these results might be the same. That is, the im- 

 mediate cause producing the shortened radial diameter and 

 usually thickened wall of the libriform cells, and the absence 

 of tracheae in the fall growth of woody tissue, might also be 

 the cause of the shortened radial diameter and usually thick- 

 ened wall of the fall growth of cork. Up to this time we 

 have used the terms fall and summer growths loosely, refer- 

 ring to the later and earlier growth of the season. Now un- 

 less it can be proven that the time of this change of growth 

 actually corresponds in both cases, it is evident there is noth- 

 ing in the above suggestion, however plausible it may appear. 

 This was attempted only in the case of Liquidambar, as the 

 two other types were not available for constant daily study. 



