168 
WRIGHT : OBSERVATIONS ON 
The Vascular Tissues,— The genus Dracæna has been the 
classic ground among monocotyledons for the study of 
sliding growth and vascular cambial activity. 
Respecting the cambial activity and the nature of the vas- 
cular bundles produced in the roots and stems of species of 
Dracæna and Yucca nothing need be said, since figures are 
so frequent in almost every text book of botany. A few 
points of general interest have been worked out, and may be 
of supplementary value to our knowledge of this group of 
plants. It will be remembered that Strasburger* worked 
mainly with the stems and roots of D. reflexa^ and Scott and 
Brebnerf with the same structures in D. fragrans, Gawl., and 
D. angustifolia^ Roxb., together with the roots of D. Draco. 
The first point of interest lay in determining the period in 
the life of the plant and the particular area at which the 
vascular cambium made its first appearance. The first indi- 
cations of a vascular cambium were obtained in a seedling 
nearly seven weeks old, and which consisted of an aerial 
shoot bearing eight comparatively small leaves, and having a 
basal diameter of 2 mm. ; the root system comprised a strongly 
branched primary root about 70 mm. in length, together with 
two young stout white roots arising from the root stock area.^ 
The cambium appeared in the pericycle of the very short 
hypocotyl immediately below the cotyledonary node, and 
from this area spread upwards into the stem and downwards 
into the primary root, where the thickenings of the endo- 
dermis helped to elucidate the origin layer of the cambial 
tissue. In the subsequent development the vascular cambium 
spreads more rapidly in the stem structures than in those of 
the root. This continues at such a rate that in seedlings 
seven months old the cambium has spread to a height of 6 cm. 
in the stem and only just over 1 cm. in the primary root. 
The products in the basal part of the stem have assumed con- 
siderable proportions,”“radial rows of three or four vascular 
bundles, — whereas in the root a continuous ring of cambium 
* Botanisches Praktikum, 2nd ed. ; Histologische Beiträge, III,, 1891. 
t The Tissues of certain Monocotyledons ; Ann. Bot. VII., 1893. 
