Arber.—On the ‘ Squamulae Intravaginales ’ of the Helobieae. 37 
on the left are free, whereas those on the right are attached to the external 
surface of the leaf, just below the level at w r hich it divides from the axis. 
Of the three squamules marked with a cross in Fig. 5 c, the two right-hand 
ones are seen fused with one another and with the axis in Fig. 5 b, which 
is cut at a level between Figs. 5 A and 5 C. The structure of the young 
squamules, at the levels of freedom and of attachment, is shown in Figs. 
TRIGLOCHIN 
Fig. 5. Triglochin maritima, L. Figs. 5 a, b, C, f, g, h, serial transverse sections from 
below upwards through young leaf, l. lt and the apical bud with younger leaves, /. 2 and /. 3 , which 
it encloses ; squamules, sq., shaded ( x 23). Fig. 5 a, margin of leaf-sheath of /. x free on left side, 
but, owing to slight obliquity of section, cut at a lower level on right-hand side, and there fused 
with axis. Fig. 5 c, section at a slightly higher level, showing three sets of squamules, external 
respectively to /. x , /. 2 , and /. 3 . Fig. 5 B shows the three squamules marked with a cross in Fig. 5 C, 
cut at a slightly lower level. Fig. 5 D, detached squamule marked with arrow to left of Fig. 5 C 
( x 193). Fig. 5 e, attached squamule marked with arrow to right of Fig. 5 c ( x 193). Figs. 5 F, 
G, h, sections through l. x and /. 2 at higher levels, to show development up to point of separation of 
ligular sheath and petiole of /. x ( x 23). 
5 D and E. A third set of squamules, external to /. 3 , are visible on the left- 
hand side in Fig. 5 c. 
(iii) The Origin of the Squamules. 
Of the plants in which we have described the ontogeny of the squamules, 
Triglochin maritima , L., is the one in which the interpretation of the facts 
observed is open to least doubt. Irmisch ( 10 ) regarded the squamules 
in this genus, not as outgrowths from the leaves, but as originating indepen¬ 
dently from the axis, but more recent writers ( 3 , 4 , 9 ) merely speak of them 
as arising in the leaf-axils. I think that the sections which I have drawn in 
Figs. 5 A, B, c show conclusively that it was Irmisch who correctly seized 
the relation of the parts. But in the light of the ‘ Leaf-skin Theory ’, 
recently put forward by E. R. Saunders ( 19 ), I think that Irmisch s concep- 
