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SCALES OF AQUATIC MONOCOTYLEDONS. 
ALISMA. 
Transverse sections of young shoots of Alisma Plantago 
exhibit an appearance such as that represented in fig. 1, Pl. 5, 
where the bases of the sheathing-leaves are seen to be separated 
from each other by numerous multicellular plates. The number 
of scales between each pair of leaves is very variable. I have 
counted as many as 27, but the usual number appears to be from 
10 to 15. The distance apart of the scales varies with the level 
of the section and the age of the shoot, and it would appear from 
that fact, as also from other evidence, that the seales in process of 
growth become divided into smaller and smaller segments. Each 
scale is an elongated ramentum-like plate (fig. 14, Pl. 6) consisting 
of one layer of slightly prosenchymatous cells, ending in a more 
orless blunt or truncated apex. The basal cells next the axil 
are parenehymatous and in early stages are merismatie. Iu 
longitudinal sections of the growing apex (fig. 3, Pl. 5, & fig. 12, 
Pl. 6) the scales are seen to be produced by segmentation of a 
single row of axillary cells, the free segments so formed them- 
selves segmenting into a distal series which gradually elongate 
to form the plate-cells, whilst the proximal eells again undergo 
division, adding to those already formed. 
Although the majority of the scales in A. Plantago arise 
singly, still not infrequently scales arise from two or more rows 
of cells concentrically placed. The appearance is then suggestive 
of a bi- or even multi-lamellar origin, until the further evolution 
of the scales is traced, when it is seen that each row has an 
independent development and results in the formation of two or 
mor: concentrically placed scales in each axil, a condition quite 
common in the allied species A. ranunculoides (Pl. 6. fig. 17), 
Rarely the separation of the initial layers does not take place for 
some time, and the bases of two and even more scales may then 
be said to show congenital fusion. In A. ranunculoides the 
normal condition, at least in the young state, is that sbowing in 
transverse section two or more rows of scales abreast, and this 
is coufirmed by examination of longitudinal sections. The mode 
of development, however, does not appear to differ from that 
just described in Alisma Plantago. Scales are entirely wanting 
between the floral leaves of both species. 
