14 MR. R. H. COMPTON: AN INVESTIGATION OF THE 
fibres and large clear cells with dark walls. The endodermis is well marked, 
and many of its cells are converted into tannin-saes, 
As we ascend into the hypocotyl the polar bands of xylem become reduced 
in bulk, and each breaks up into a median protoxylem and a pair of meta- 
xylems: the triads so formed remain in close association, Each lateral 
primary xylem also divides into two halves along the minor axis, and these 
separate tangentially and move outwards towards the metaxylem groups of 
the polar triads, with which they fuse in pairs. This process is only com- 
pleted just below the node, but the short hypocotyl has throughout a stem- 
like structure save for the crushed polar protoxylems. 
The passage from diarchy to tetrarchy is of interest, and may be compared 
with the similar phenomenon in Liriodendron tulipifera, also an arboreal 
species (Thomas, 1907, p. 81). The occurrence of diarchy in the Bauhinieze 
has already been recorded by Van Tieghem and Douliot in Cercis (1888, p. 173). 
The structure of В. yunnanensis agrees closely with other Bauhiniez with 
short hypocotyls, when once tetrarchy has been attained. 
BAUHINIA TOMENTOSA, Linn. (РІ. 3. figs. 42-45.) 
Hypocotyl narrowing gradually to root. Cotyledons ovate, thin. De 
Candolle (1825, pl. 26) and Lubbock (1892, i. p. 463) give figures of the 
seedling. 
The slenderest species of Bauhinia examined. The type of transition is, 
however, identical with that of other species, except that the transition- 
changes are shifted slightly higher up the hypocotyl. The root is tetrarch, 
with a fair-sized pith (fig. 42). The position of fig. 43 is reached at the 
collet, and of fig. 44 about a quarter of the way up the hypocotyl, The 
diagrams are taken from this species, though they apply equally well to other 
Bauhinia spp. (p. 15). 
BAUHINIA RACEMOSA, Lam. (РІ. 3. figs. 38-41.) 
Shrub or small tree. Cotyledons on the surface of the ground. Hypo- 
cotyl narrowing gradually to a long root. Cotyledons ovate. 
The root shows variability in the number of protoxylems, but six appears 
to be the normal number. The processes of transition in hexarch seedlings 
are best understood from the diagrams. Fig. 38 shows the condition at 
1:5 mm. below the collet. At the collet the xylem ring has broken into six 
bands arranged tangentially, each with one of the protoxylems (fig. 39). 
The division, however, has not occurred symmetrically, but has taken place 
as indicated by the dotted lines in fig. 38. The two bands in the cotyledonary 
plane and two others are double, with the protoxylem median : the remaining 
two have their protoxylems on the edge towards the intereotyledonary plane. 
Fig. 40, showing the condition half-way up the hypocotyl, indicates the 
destiny of the several bundles. All the protoxylems are cotyledonary, and 
so are the metaxylems with the exception of two groups, indicated by cross- 
