154 Transactions. — Botany. 



euticularised (fig. IX.), but there appears to be no forma- 

 tion of phellogen. The cortex is here modified, and in its 

 inner lavers appear spaces, crossed by bands of cells. These 

 spaces, like those of the stem, contain resin ; but their forma- 

 tion is less regular. They are formed by the separation of 

 the cells of the cortex, with less regular divisions. The form 

 of the vascular cylinder is rounded at this stage. The 

 phloem-band is regular and broad, the outer layers consisting 

 almost entirely of parenchyma and sclerenchymatous cells 

 with greatly thickened, pitted walls. The xylem consists 

 wholly of thick-walled elements, as in the older stem. The 

 pith, too, has thickened, pitted walls (fig. X.). In a still 

 older root there is no phellogen, and no regular formation of 

 cork ; but the cells of the cortex become euticularised in a 

 centripetal direction. This process continues into the outer 

 cells of the phloem layer, the cortex with its resin-passages, 

 peeling off as bark. The outer layers of phloem consist, 

 in large part, of masses of sclerenchyma, and these extend 

 deeply into the tissue of the phloem. 



Leaf. 



The leaf is |^in.— |in. in length. The tip is as broad as 

 the leaf is long, tapering towards the base (fig. IX., A, B). 

 At its base it is thin and membranous, at its tip thick and 

 fleshy. Into each leaf there enter three vascular bundles, 

 or sometimes four (fig. III.), closely resembling those of the 

 stiem, except that they are closed; they are accompanied by a 

 resin-passage, continuous with those in the stem (fig. III.). 

 Near the base the leaf is composed of a compact tissue of cells, 

 rounded in form and colourless, with the exception of a single 

 layer of cells on the under-surface next the epidermis, which 

 contain a few chlorophyll grains. Around the bundle there is 

 a layer of cells similar to those of the mesophyll, but smaller. 

 The epidermis of the lower surface contains a few stomata 

 (fig. XII., St.). The cuticle is only slightly developed, and 

 some of the epidermal cells on the under-surface are observed 

 to grow out into long, multicellular hairs. 



Towards the base of the leaf the three bundles branch 

 once or twice, but when they reach the fleshy green tip they 

 break up into a close network. In this fleshy tip lies the 

 greatest peculiarity of the plant. Stripped of hairs and 

 examined on the upper side it exhibits a great number of 

 projections of tissue (fig. XI., E). On the lower side (F) it 

 has corresponding depressions in its surface, so the projections 

 are of the nature of bags of tissue. 



This part of the leaf has a very slightly euticularised 

 epidermis, with many stomata on the upper and under sur- 

 faces. The mesophyll has the cells of the upper surface 



