OF THE WOOD OF INDIAN SPECIES OF PINUS. 46; 
near each pit. The thickenings are seen to be separated from the actual pit 
by a short stretch of wall. These thickened parts of the middle lamella 
differ somewhat from tle middle lamella elsewhere in. chemical composition, 
for they do not stain crimson with phloroglucin and hydrochloric acid, 
whereas elsewhere the middle lamella is thinner and does stain more or 
less. Tangential sections stained in safranin and mounted in Canada 
balsam show these thickenings unstained and appearing like empty inter- 
cellular spaces, because their refractive index agrees with that of the balsam, 
whereas the rest of the middle lamella may be quite distinct. Stained 
with methylene-blue succeeded by 2 per cent. acetic acid or ruthenium- 
red (especially after being swollen by successive treatment with hydrochloric 
acid and ammonia) they stand out from the rest of the wall as more deeply 
stained parts of the middle lamella (fig. 38), though the other parts of this 
also frequently stain with ruthenium-red. In transverse. section treated with 
ruthenium-red Sanio’s rims are seen as deeply stained lines in the middle 
lamella of the radial walls, and contrast with the scarcely stained middle 
lamella in the tangential walls or in radial walls where the rims are lacking. 
(In our specimen a number of the tracheids in contact with medullary 
‘avs showed in transverse section the inner layers of the tangential walls, 
and sometimes of the radial walls, delignified and staining with ruthenium- 
red. Tangential sections showed that this is due to the occurrence of patches 
of pectic substance situated at the levels of the medullary rays. This localized 
pectic lining is due to the action of a fungus which is mainly distributed in 
the medullary rays into the adjoining tracheid, which run mainly in a 
tangential transverse direction.) 
Combining the above given facts with Sanio’s account of the development 
of pits in primary pit-areas, the following would therefore appear to be the 
truth. When young the actual marginal portion of the primary pit-area does 
not thicken by deposits of lignified wall so soon as it does elsewhere (except 
on the pit-closing membrane) but thickens by successive deposits of pectic 
substance until a stage is reached when lignified wall-substance is deposited 
even over the now thickened rims of the primary pit-area. Sanio’s rims 
represent a system of rod-like or band-like pectic thickenings of the middle 
lamella running transversely in the radial walls and linked here and there by 
slightly curved longitudinal band-like similar thickenings (representing the 
lateral margins of the primary pit-areas). 
In tracheids at the junction of the spring- and summer-wood, where the 
pits are uniseriate, Sanio’s rims as seen in radial section are reduced to little 
crescent-shaped areas in a median position above and below each pit, and not 
as broad as the pit (fig. 44). In the summer-wood outside this critical layer 
Sanio’s rims are not to be seen in radial section, even after staining with 
ruthenium-red. In tangential section the middle lamella here does not dilate 
