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DESCRIPTION of plates XXV AND XXVI. 
Illustrating Dr. Darbishire’s paper on Mamillaria. 
a— phloem. 
b = spiral tracheid. 
c — storage tracheid. 
d — hypoderma. 
e — epidermis. 
f= palisade* tissue. 
g = phellogen. 
h = air-containing fibres. 
i = hairs. 
k = cork. 
/=protoxylem. 
m = metaxylem. 
n = wood-parenchyma. 
0 = protophloem. 
/ = cambiform cells. 
^ = libriform cells. 
PLATE XXV. 
r— cambium. 
s = cortex. 
^ = thick -walled fibres. 
u = medullary ray. 
v = spine-primordium. 
w — tubercle-primordium. 
x = axillary bud. 
y — cuticle. 
z — intercellular space. 
Fig. 1. Photograph of clump of Mamillaria elongata , taken in the succulent House, Royal 
Botanic Gardens, Kew. Slightly reduced. 
Fig. 2. Transverse section across main axis of young plant. The vascular bundles are seen to 
be cut across in the centre. Near the margin are the projecting tubercles and the paraheliode con- 
sisting of spines, x 3. 
Fig. 3. A complete young plant in longitudinal section. The root and shoot are seen, and in 
the latter again the tubercles, spines, and vascular bundles, x 3, 
Fig. 4. Central bundle of a tubercle, cut across low down in the latter. To the inside of the 
bast ( a ) is the wood ( b ), to which four storage tracheids (c) have been added centripetally ; air-spaces 
( z ) are also seen, x 160. 
Fig. 5. Two central bundles cut across higher up. The bast (a) and the smaller wood-cells (3) 
are seen. To the latter numerous storage tracheids ( c ) have been added ; air-spaces (z) are also seen. 
X 160. 
Fig. 6. Three central bundles just underneath the paraheliode set of spines. The last has 
disappeared ; the spiral tracheids ( b ) of the old wood and the new storage tracheids ( c ) can be dis- 
tinguished. x 160. 
Fig. 7. A cortical bundle cut transversely low down in the tubercle. The bast ( a ), the wood 
(£), and a large storage tracheid at the inner side, x 430. 
Fig. 8. The ending of a cortical bundle higher up. The bast has disappeared and two storage 
tracheids (V) alone are visible, x 430. 
