igi2] BROWN— PINUS RIGIDA 389 



ber of cutting, and tree, and kept separate from the others in all 

 the successive processes of fixing and inibedding. 



The following year (1910) cuttings were again resumed on the 

 same trees, as well as on four more in the same row. The manner 

 of procedure was identical with that above described except 

 (a) every other cutting was omitted and.{b) this season the first 

 cutting was made February 21, the second April 2, and thereafter 

 xmtil the third of May. The object was to check up the results of 

 the previous season and to make new observations. Two cuttings 

 were also made on trees A, B, and C on April 27, one on the north 

 side and one on the south. For purposes of comparison, one root 

 cutting was taken from tree III on the same date. 



Microscopical characters of the wood 



As is characteristic of the Coniferae, the secondary wood of 

 Pinus rigida is entirely devoid of vessels. It consists almost 

 entirely of tracheids with bordered pits on their radial walls. In 

 cross-section these appear regularly arranged in radial rows, which 

 occasionally divide as they proceed toward the cambium. In 

 longitudinal section they present the normal tracheid form, that is, 

 a rectangular prism with sloping ends. The annual rings are 

 sharply differentiated. Proceeding from, the pith outward in 

 radial direction are numerous pith rays; secondary rays arise in 

 response to necessity; both are of the usual coniferous tj^e. The 

 histological characters of coniferous wood, however, have been 

 described in detail by Penhallow (ii), and the reader is referred 

 to his excellent work for further detail. 



The structure of the secondary thickening in the roots is quite 

 closely related to that of the stem. However, there are one or. 

 two differences. The demarcation between the different rings is 

 not so sharp. This results because the wood of the root is less 

 dense than that of the stem. The tracheids possess wider lumina 

 and there is less siunmer wood produced. In radial section the 

 bordered pits on the walls are often biseriate, a condition which is 

 never met with in the wood of the aerial portion. 



