40 A rber.—On the ‘ Squamulae 1 ntravagi nates' of the Helobieae. 
region. I am not aware that the existence of squamules in such a position 
has ever been recorded, but though their discovery at the junction of 
hypocotyl and radicle would be a strong confirmation of the views 
expressed in this paper, I do not think that these views are necessarily 
discredited by their absence. For in the exposed position which the 
‘ collar ’ presents—unprotected by the leaf-sheaths which enclose the base 
of every other internode—the tendency to the formation of squamules may 
well be held in abeyance by the absence of the requisite physiological 
conditions. 
If the squamules throughout the Helobieae are, as seems probable, 
dorsal basal appendages of the leaves, it becomes unnecessary to discuss the 
idea that they are stipulac intrafoliaccae (Caspary, 5 ), or the more recent 
suggestion that in the case of the Alismataceae they are ligular structures 
(Buchenau, 4 ). For neither stipules nor ligules are ever found on the dorsal 
surface of the leaves to which they belong. The case of the Alismataceae 
must, however, be treated as an open one for the present, since we have no 
exact information as to the origin of the squamules in this Family ; it is, of 
course, probable that they arise in the same way as in the other Helobieae, 
but this cannot be assumed without proof. I have examined serial sections 
of buds of Sagitiaria sagittifolia , L., from this point of view, but the thin¬ 
ness of the squamules, the extreme abbreviation of the internodes, and the 
crowding of the young leaves have, so far, prevented my arriving at any 
certainty as to the way in which the squamules originate. 
(iv) Summary. 
From a study of the origin of the squamulae intravaginales in Potamo- 
geton and Cymodocea (Potamogetonaceae) and Triglochin (Scheuchzeria- 
ceae), it is concluded that these structures are not appendages of the leaf in 
whose axil they are found—as has often been assumed—but that they 
originate from the surface of the internode separating this leaf from the next 
leaf above. The records in the literature indicate that this is also true for 
the Hydrocharitaceae, Aponogetonaceae, and those Araceae which possess 
squamules. In terms of the ‘Leaf-skin Theory’ of E. R. Saunders ( 19 ), 
the squamules should therefore be described as outgrowths from the down¬ 
ward, axis-clothing prolongation of that leaf whose level of exsertion comes 
next above their place of origin. 
Balfour Laboratory, 
Cambridge. 
