1889. J BOTANICAL GAZETTE, 41 



Sections cut from different Liquidambar U\ s. at different 



dates along the course of the summer's growth, and extend- 

 ing late into the fall, proved that the narrowing of the wood 

 cells occurred at the same time as that of the cork cells. 



The work was begun too late in the season for the examina- 

 tion of the beginning of growth in the spring-time. Exact 



correspondence in time is not necessary, however, in case of 

 the beginning of spring growth. Even were it proven that 

 the real cambium resumed its activity a few days earlier or 

 later than the cork cambium, this is no argument against the 

 above hypothesis of the same cause acting on both kinds 01 

 cambium after both have been active during the summer. 



Perhaps a partial apology should be made for offering 

 the suggestion, as it seems hardly possible that this change 

 from summer to fall growth in cork formation, which has so 

 often been given as one of the important characteristics of 

 cork, should not have been used in the recent investigations 

 about the question of annual rings of wood, unless this ques- 

 tion of correspondence in time had been thoroughly tested 

 and found to fail. In all the recent literature to which I 

 have had access I have found but one allusion to this, that is 

 in the article by Gerber, before referred to. He says : M The 

 early and late cork is like summer and fall wood, but that 

 the time of their formation is not the same." Then he ex- 

 plains that the time of the beginning of the formation of the 

 pring wood does not correspond with that of the formation 

 of spring cork, but savs nothing whatever respecting the 

 time of beginning of fall growth. 



In connection with this, a brief summary of the views 

 about the cause of the difference between the spring and fall 

 wood may be excused here. Sachs's theory, stated in the 

 first edition of his text-book, was that the peculiarity of the 

 fall wood was due to the increased pressure of the rind 

 at that time. Later experiments have failed to support this 

 view. Among the first objections to this theory was the fre- 

 quent occurrence of double year's ring. An article by 

 Prof, Knv 7 on this subject, written in 1880, contains a state- 

 ment of previous authorities, together with his own investi- 



gations, showing conclusivelv that double year's rings occur. 



Russow, 8 in an article in 1881, speaks against the theory of 



7 L. Kny Verdoppelung des Jahresring. Verhaudlung d. bot. Vt: reins der Provinz 

 Brandenburg, 1880. p. 1. 



8 Ru iff, Entwickelung det Hoftiipfels der Membrau tor Hoi ellenund desJahre 

 ringes bei den Abietineen. Sitzungsber. d. natur. Ges. Dorpat, 1881. Hd. 6. Heft. 1. 



