100 THE BOTANICAL MAGAZINE. [Vol. xxxit No. 403. 



SECTION II 



Dimensions of xylem-elements 



A. Size of tracheidal cells of coniferous wood 



For comparison of dimensions of xylem-elements it will be 

 convenient to use the homologous elements such as tracheid of conifer- 

 ous wood. Sanio 1 studied the length of tracheidal cells of Pinas 

 sylvestris and formed five laws, of which the first two will be quoted 

 here : — 



1. Die Holzzellen nehnien in den Stamm- und Asttheilen iiberall von Innen 

 nacli Aussen durch eine Anzahl von Jahrringen hindurch zu, bis eine bestinimte 

 Grosse erricht ist, uelche dann fur die folgenden Jahrringe constant bleibt. 



2. Die endlich constant Grosse der Holzzellen andert sich in Stamm in der 

 Weise ab, dass sie stetig von Unter nach Oben zunimmt, in bestimmten Hohe ihr 

 Maximum erreicht und dann nacli Wipfel zu wieder abnimmt. 



As regards the first law, he ascertained that the length of 

 tracheidal cejls increased with succeeding annual rings, until about 

 the fortieth ring, beyond which it remained constant. As to the 

 second law, the length of tracheidal elements of the same age increases 

 with the height until it reaches the maximum at the height of 21.5 

 feet above the ground, whence it decreases upwards again. Bailey 

 and Shepard 2 measured the length of tracheidal cells in pine, fir, 

 hemlock and others. According to them, the second law was found 

 to hold good, but the first law was not strictly correct, for the 

 length did not become constant at the fortieth ring but increased 

 further. 



B. Length of tracheids 3 in Cryptomeria japonica 



Small blocks of wood were taken from certain annual rings and 

 tracheids were isolated by Schultze's macerating method. Out of 

 the numerous tracheids in the field of the microscope, their maximum 

 and minimum real lengths were determined, and the average of the two 

 was taken for the length of tracheidal cells of that annual ring, as done 



1. Sanio, C. (1872) Ueber die Grosse der Holzzellen bei den gemeinen Kiefer. 

 — Jahrb. f. Wiss. Bot., Bel. 8. 



2. Bailey,' I. W. and Shepard, H. B. (1915) Sanio's laws for the variation in 

 the size of coniferous tracheids. — Bot. Gaz., vol. 60. 



3. The term " tracheids " was used in the present paper in the sense of tracheidal 

 cells, as is usually done by most authors, when there was no liability of misunder- 

 standing for the tissue tracheid. 



