Arbcr. — On the ‘ Squamulae Iutravaginales ’ of the Helobieae. 33 
are seen. A still younger leaf (pet. ?j and tig. s..t) has further squamules 
(sq. c) within it, surrounding the developing apex (ap.). In Figs. 1 C and 
D, the changes which are passed through by this growing-point, between, the 
level of Fig. 1 A and the tip of the shoot, can be followed. Fig. 1 c shows 
another leaf (/. 4 ) and a further set of squamules (sq. d), while in Fig. 1 D 
POTAMOGETON 
Figs, i and 2. Potamogeton sp. (broad-leaved, submerged form). Fig. i A, transverse section 
of inner part of apical bud ( x 47) ; in case of outermost leaf represented, only the ligular sheath 
(lig. with its keels ( k . and k'.) are shown ; limb ( lam.. 2 ) and ligular sheath (lig. s. 2 ) of second 
leaf; petiole or base of limb (pet.p) and sheath (lig. s. 3 ) of third leaf; ap ., shoot-apex. Three sets 
of squamules (shaded), sq. a, sq. b , sq. c, are seen outside second leaf, third leaf, and apex respectively. 
Fig. 1 B, transverse section of squamule marked with arrow in Fig. I A (x 193). Figs. 1 C and D, 
changes in shoot apex ( ap. of Fig. 1 a) as tip is approached (x 47). Fig. 1 c, fourth leaf (/. 4 ) 
detaching itself from apex, and squamules (sq. d) occurring between it and apex. Fig. I D is close 
to tip of shoot, and shows highest leaves (1. 5 and /. 6 ) on either side of apex (ap.). Figs. 2 a-h, 
series of transverse sections from below upwards through three successive young leaves and growing- 
point of another bud ( x 47); sections broken on side towards petiole of leaf 1, so this region recon¬ 
structed; lettering as in Fig. 1 ; sh x and sh\, margins of sheathing leaf-base. 
the extreme apex of the axis is reached (ap-), lying between the two 
youngest leaves (/.- and /. 6 ). The set of squamules within leaf 4 in Fig. 1 c 
are the youngest to be found in this shoot ; I cannot with certainty detect 
any inside leaf 5 or leaf 6. 
The sections drawn in Figs. 1 A-D are too far above the bases of most 
of the leaves to give much enlightenment on the origin of the squamules: 
for this we must turn to Figs. 2 A-H, which represent sections from a series 
D 
