52 PROFESSOR THISELTON DYER. 



The screw pines derive their name from the arrangement 

 of the leaves in three close spirals at the extremities of the 

 branches. As the leaves fall off below, they leave narrow, 

 almost annular scars upon the stem, closely approximated 

 together, and dotted with the cicatrices of the vascular 

 bundles. The exterior of the stem is, in other respects, 

 smooth, and covered with a very thin, rather corky rind, 

 composed of rows of tabular cells, the outermost filled with 

 very opaque incrusting matter. The general parenchyma of 

 the stem does not appear, at any rate in the stems of the age 

 which I examined, to becom'e indurated, but remains succu- 

 lent. The walls of the cells, though thin, were slightly 

 thickened, and were evidently furnished with rather large 

 " pores." The form Avhich the cells take rather depends upon 

 their position ; as is also the case in palms, the cells are 

 manifestly compressed when they are situated between two of 

 the bundles. In this position they are really homologous 

 with the compressed parenchyma of a "medullary ray." 

 The most external portion of the parenchyma, abutting on 

 the tabular cells of the rind, appears to retain its vitality, 

 and the cells contain sparingly chlorophyll-corpuscles. 



A transverse section of a stem about an inch and a half in 

 diameter shows a sharply defined cortical region about two 

 lines broad, in which the bundles are destitute of ducts and 

 are exceedingly attenuated. Within this region, on the 

 contrary, the bundles are crowded together very closely, and 

 are very conspicuous. It might be supposed that this so- 

 called cortical region is, in reality, the result of such a 

 circumferential growth as has been described in Dracana. 

 But the fibrous bundles which it contains appear to me to 

 terminate obliquely in the rind, and not to run parallel to it, 

 as they would do in the former case. Perhaps these bundles 

 are identical with the evascular bundles which Millardet 

 describes in Draccena under the name of " peripheral," 

 distinijuishinff them from those connected with the leaves, 

 which he calls " axile." They pursue a much straighter 

 course than these last, and are developed later. Millardet 

 believes that they will be found in all monocotyledons. 



The areas of the fibro-vascular bundles in a transverse 

 section increase regularly in size, proceeding inwards. The 

 bundles consist of amass of liber cells externally, of the usual 

 elongated form ; internally there is a much smaller mass, 

 consisting of vessels or ducts and cells shorter than the 

 external liber cells, with oblique and sometimes quite hori- 

 zontally truncate ends. Moljl has described these, in palms, 

 as wood-cells. They are marked with distinct pores, and in 



