936 Lee. — Notes on the Anatomy and Morphology of 
like trichomes are found 1 ). The trichome of P achypodium usually consists 
of a multicellular base from which radiate a number of straight hairs, which 
have walls cuticularized like those of the epidermis, and well-marked nuclei. 
Near the apex unicellular hairs are common. The trichomes tend to pass 
into emergences which consist of several cells, varying in number from 
6 to io, arranged in a manner similar to that found in the trichomes, but 
possessing a massive stalk, in the formation of which the subepidermal cells 
take part (Text-fig. 8). Examples of these structures can be seen forming 
a regular series ranging from unicellular hairs to stellate trichomes and 
emergences. 
The structure of the leaf is very compact, the mesophyll showing prac- 
tically no differentiation into palisade and spongy tissue (Fig. 13). It 
is made up of oblong cells with well-marked nuclei, compactly arranged 
Text-fig. 6. Outline of leaf in transverse section, 
showing the lamina bent up on either side of the 
midrib. 
Text-fig. 7. Longitudinal section 
of a stoma. 
except underneath the stomata, where there are large stomatal chambers. 
The cells underneath the upper epidermis are usually somewhat longer and 
more compactly arranged, forming a tissue slightly resembling palisade, in 
which there are no sclerosed cells such as are sometimes present in members 
of the Apocynaceae. 2 Calcium oxalate is present in the inner cells in 
crystals similar to those in the stem cortex. The vascular bundles are 
collateral, have no cambium, and are smaller than those in the stem 
(Fig. 13). They are accompanied by one or more laticiferous cells (d, 
Fig. 13) which are similar to those found in the stem, but here are never 
found apart from the bundles. 
The bundle of the petiole is arc-shaped in transverse section (Text- 
fig* 3 )* The xylem (a, Fig. 5) forms a band interrupted by parenchyma ; 
the phloem (b, Fig. 5) forms a band of very small sieve-tubes with sieve- 
1 Solereder (5), p. 530, Fig. 121, 
2 1. c., p. 529. 
