OF THE WOOD OF INDIAN SPECIES OF PINUS. 411 
The bordered pits on the radial walls are uniseriate though occasionally 
they occur in pairs. In contour the pit-chamber is oval or circular (fig. 6), 
the former especially often in the spring-wood, whilst the aperture in the 
inmost spring-wood is circular or slightly oval with the longer axis transverse; 
but travelling outwards in the ring the aperture becomes gradually oblique 
or even vertical (Pl. 24, fig. 8), broadly lenticular, not becoming narrow 
lenticular except perhaps in the outermost layer. Moreover, the pointed ends 
of the aperture are continuous with oblique line-like furrows which may 
he continuous with like ones from higher and lower pits, so that the spiral 
arrangement of the pit-apertures is very evident. (It is possible that these 
line-like furrows are not natural to the wood in the tree, but are due to 
desiccation and consequent fracture.) The longitudinal distance apart of the 
pits in the spring-wood is very variable in tracheids, алох rims are distinct. 
The outer summer-tracheids also possess on their tangential walls smaller, 
more irregularly arranged, bordered pits, which are scanty and uniseriate in 
some tracheids, and more numerous and up to triseriate in others. They are 
most numerous in the outermost two or three layers, but occur in the latest 
five series of tracheids. In any case they occupy a relatively small area of 
the wall, and agree in structure and approximately in size with the pits on 
the radial walls of the summer-tracheids : the outline of the chamber is 
circular and that of the orifice is lenticular (fig. 7) 
j* 
Resin-Ducts. 
The duets attain a diameter of 120 д and their epithelial cells a radial 
width of 144. The flattened epithelial cells give rise to numerous occluding 
thyloses. Around these are two layers of rather flattened parenchyma with 
somewhat thicker pitted walls, which are longer and haye their thinnest 
walls towards the resin-epithelium. These are succeeded on the outside by 
parenchymatous cells which are oblong rectangular in longitudinal section 
and have thicker walls; and these in turn by parenchyma-tracheids of 
similar shape with relatively thin walls and few bordered pits which occur 
on the end walls as well as on the lateral, including tangential walls in 
summer-wood and spring-wood (fig. 2). The lengths of measured paren- 
chyma-tracheids were ‘114, :25, +27, and *5 mm., in comparison with 3 mm. 
the approximate length of the ordinary tracheids. Thus around the resin- 
duets there are cells showing transitional stages from epithelial parenchyma 
to typical tracheids. 
Medullary Rays. 
The linear usually uniseriate rays vary in height from 1 to 24 cells. The 
fusiform rays attain a height equivalent to 30 cells, but some of them are 
shallower than the tallest uniseriate rays. 
