52 BOTANICAL GAZETTE [TANUARY 
Fig. 1 shows a transverse section of the wood of Aesculus Hip- 
pocastanum L., and fig. 2 a tangential section of the same. From 
these it is possible to make out the main features of the wood. 
Woods may be grouped into three classes, depending on the dis- 
tribution of parenchyma: (1) a primitive type with only terminal 
parenchyma on the “face of the summer wood”; (2) a more 
advanced type with parenchyma scattered throughout the year’s 
growth, that is “‘diffuse’’; and (3) the highest type with parenchyma 
only around the vessels, or “vasicentric.”’ Aesculus belongs to the 
third of these groups; furthermore, its parenchyma is chiefly on 
the tangential wall of the vessels. The mechanical elements of 
the wood also exhibit a high degree of specialization, in that they 
are all transformed to libriform fibers, with characteristically 
thick walls, and narrow, obliquely elongated simple pits. The 
vessels are scattered throughout the year’s growth, giving the 
‘‘diffuse porous effect.’’ The vessels have pits on the side walls 
closely crowded together, but never fused, end walls with porous 
perforations, and tertially spiral thickenings on their inner walls. 
Thus in having vasicentric parenchyma, libriform fibers, and 
vessels with porous perforations, Aesculus has the wood structures 
_ characteristic of the highest dicots, but the rays present a pecul- 
iarly simple condition. They are always of the linear, uniseriate 
type, like those of many of the gymnosperms. 
Figs. 1 and 2 represent Aesculus Hippocastanum, but the wood 
is practically indistinguishable from that of its near relative 
Aesculus glabra Willd., as well as other species of the genus, and 
this description applies equally to all. 
Fig. 3 represents a tangential section of Acer saccharum Marsh. 
The wood is ‘‘diffuse porous” like that of Aesculus, and the pa- 
renchyma is likewise vasicentric, but less abundant, and instead of 
being on the tangential wall, it is on the radial wall. The libriform 
fibers are heavier than those of Aesculus, especially those imme- 
diately around the vessels, which are very thick walled, while those 
in the intervals are larger and thinner walled. The vessels are 
very similar to those of Aesculus, having porous perforations 0m 
the end walls, densely crowded pits on the side walls, and well 
marked tertiary thickenings. The rays, however, are strikingly 
