20 P. ORPEN BOWER. 
EMistology of the Seedling. 
If transverse sections be cut of the hypo-cotyledonary 
stem of the seedling, the tissues will be found to be ar- 
ranged in the following manner :—At the periphery of the 
section is an epidermal layer with cuticularised outer walls. 
Here and there are stomata, which demand no special notice 
beyond their guard cells being slightly depressed. Beneath 
the epidermis is a fairly regular cortical tissue, in which, 
after treatment with alcohol, are found large quantities of 
the sphere crystals of inulin. The outer layers of cells of 
the cortical tissue have, in some cases, cuticularised walls 
(figs. 11, 12). Scattered irregularly through the cortical 
tissue, but more especially towards the outside are scleren- 
chymatous cells. These occur singly, or in groups of two 
to five or six. This sclerenchyma is not very constant in 
quantity, and was in some cases found to be absent. To- 
wards the centre of the section will be found four fibro- 
vascular bundles, arranged as in fig 11. They are peculiar 
in having the xylem portion turned towards the periphery, 
and the phloem towards the centre of the stem. Moreover, 
the xylem tails off laterally in a manner represented in fig. 
11 by the lines marked pr, zy. 
The structure of the individual bundle corresponds pretty 
closely with that of the leaf as described by De Bary,' 
although not so complicated. 
On reference to fig. 13, which represents the fibro-vascular 
bundle of the young hypo-cotyledonary stem before exten- 
sion takes place, it will be seen that the first developed 
xylem elements are drawn out into a long lateral series. 
Development begins at the end of this series, marked pr, zy. 
and progresses in the direction shown: by the arrow. The 
further development of xylem occurs only opposite the later- 
formed elements, marked ay, fig. 13. A layer of cells 
(cb) have already begun to divide as a cambium layer; and 
the cells between this and the already formed xylem are 
beginning to thicken their walls, and develop into xylem 
elements. The group of cells, with very small cell cavity, 
on the central side of the cambium layer, are the protophloem 
(pph, fig. 13). 
We shall now be in a position better to understand the 
mature bundle. Fig. 14 represents a section through a 
fibro-vascular bundle taken from a hypo-cotyledonary stem 
which is fully extended. Here the protoxylem elements 
will be seen to have been drawn out thin by the extension 
1 ¢Vergleichende Anatomie,’ p. 347. 
