832 Yapp . — Spiraea Ulmaria, Z., and its Bearing on the 
on the larger veins at approximately the same time as the protoxylem, and 
while the leaf is still completely enclosed in the bud (Text-fig. 7). At this 
time the remainder of the lamina is meristematic, though the upper and 
lower epidermis and several layers of mesophyll are distinguishable. 
A somewhat later stage is diagrammatically represented in Text-fig. 8, a. 
The first seven leaves of the shoot had expanded, but the leaf figured was 
still completely enclosed in the bud. The interveinal parts of the lamina 
Text-fig. 8. A, transverse section through part of an apical bud, showing several leaflets of 
a single developing leaf. Meristematic portions shaded black. B, a single leaflet just emerged 
from the bud. c, a still later stage. All x 16. 
are developing, and in consequence assuming a looped appearance. They 
are still meristematic, and as yet bear no hairs. The mesophyll is un- 
differentiated, and there are neither stomata nor intercellular spaces. The 
smaller veins have not yet been formed. In the main veins the protoxylem 
alone is lignified, but the veinal hairs are now so numerous that they form 
a fairly dense packing below and between the veins. 
Text-fig. 8, B is taken from the terminal leaflet of the ninth leaf of the 
