96 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



the exterior of the completed growth layers remains as postseasonal 

 growth. For instance, TTC 12-12 was sectioned on July 31, 1944. 

 Sections a, 23 cm. from the tip, possess for 1944 two sharp, complete, 

 entire growth layers and a hint of added xylem on the long radius. 

 Sections h (pi. 10, fig. i), 14 cm. from the tip, possess for 1944 two 

 sharp, complete, entire growth layers, a sharp lens, and a diffuse lens 

 in addition to several lenses of immature xylem one cell thick. Sec- 

 tions c, 2.5 cm. from the tip, have for 1944 two sharp, complete, en- 

 tire growth layers plus single cells scattered around the circuit. Such 

 added growth is a phenomenon not at all uncommon on branches sec- 

 tioned in midsummer, either on gymnosperms or angiosperms. 



Much additional information has been obtained from sections taken 

 along a branch. A series of branches, TTP 24-13 to 24-15 and 24-23 

 to 24-25, was cut January i, 1943. Two representative specimens will 

 illustrate the series. In TTP 24-13-a, 53 cm. from the tip, the incre- 

 ment for 1942 contains one sharp, complete, entire growth layer, di- 

 vided densewood, and added xylem of thin concurrent lenses com- 

 posed of one to two rows of immature cells. Sections b, 41.5 cm. from 

 the tip, contain one sharp, complete, entire growth layer, a diffuse lens, 

 and many narrow lenses of immature cells extending in a series almost 

 continuous around the circuit. Sections c, 30 cm. from the tip, contain 

 the same sequence for 1942 as b except for the lack of postseasonal 

 growth. In TTP 24-24-a, 15 cm. from the tip, the increment for 1942 

 contains one sharp, complete, entire growth layer. Sections b, 9.5 cm. 

 from the tip, and c, 6.3 cm. from tip, contain, in addition to one sharp, 

 complete, entire growth layer, postseasonal growth of several concur- 

 rent lenses composed of one or two rows of immature cells. Sections 

 d, 0.3 cm. from the tip, show merely slight evidence of added growth. 



There remain, in the discussion of the present type of postseasonal 

 growth, three examples of special interest. The so-called Conserva- 

 tory trees were moved indoors November 16, 1939, from the grounds 

 of the Experiment Substation. Tip growth appeared to be in progress 

 to a slight extent on November 29. As regards the sections cut on that 

 date, there was no doubt that the trees were laying down cells of post- 

 seasonal growth. Specimens of the different trees, Arizona cypress 

 (Con C), ponderosa pine (Con P), and loblolly pine (Con T), agree 

 in showing added xylem of isolated cells, incomplete concurrent lenses, 

 or an incomplete, entire growth layer. After a short time we came to 

 look for the "Conservatory growth layer" because it was so character- 

 istic of all specimens, no matter whether they were cut in late 1939 

 or any time up to 1945. The evidence indicated that the trees were 

 stimulated into growth by removal to the Conservatory and that there 



