CHAP. I. 
VASCULAR TISSUE. 
21 
becoming visible; and, finally, they may sometimes be de- 
tached from the tissue (Plate II. fig. 7.), or fall away spon- 
taneously. In the latter case they leave a hole in the tissue at 
the place where they grew; and holes thus occasioned misled 
Kieser into the belief that the woody fibre of Ephedra was 
really pierced with pores of considerable magnitude. An 
illustration of the manner in which these perforations are 
caused will be found in Plate II. fig. 7. 
A different explanation is given by Mohl, whose observa- 
tions have been confirmed by Unger. In the opinion of these 
anatomists, the supposed glands of coniferous tissue are circu- 
lar spaces, where the membrane of the tube becomes abruptly 
extremely thin ; and it is said that transverse slices of coni- 
ferous wood, made at an angle of 45*^, demonstrate the fact. 
Adolphe Brongniart has rightly stated, that there exists in 
Gnetum Gnemon a form of tissue exactly the same as in 
Coniferae. [Voyage de Freycinet.) In a species of that genus 
collected in Tavoy by Dr. Wallich, the glands are very con- 
spicuous. (Plate II. fig. 5.) 
Woody tissue constitutes a considerable proportion of the 
ligneous part of all plants ; it is common in bark, and it forms 
the principal portion of the veins of leaves, to which it gives 
stiffness and tenacity. 
Sect. III. Of Vascular Tissue, 
6 7 8 9 
Vascular tissue consists of simple membranous tubes ta- 
pering to each end, but often ending abmptly, either having 
c 3 
