232 BOTANICAL GAZETTE [MARCH 
SumMARY.—The general situation obtaining in seedling oaks 
and wounded stems may be seen by referring to text fig. 4, which 
is a schematic representation of a wounded oak stem, and illustrates 
the position of reversionary features on the edge of the wound cap. 
These reversionary rays are represented by a series of parallel lines, 
in contrast with the compound rays, which are solid black. Trau- 
matic aggregate rays occur in the wound cap itself, and laterally 
they pass over into the normal compound type. A comparison 
with text fig. 3, representing a wounded birch stem, brings out the 
important difference in respect to wound reaction and the position 
of traumatic features in Betula and Quercus. The transition from 
aggregate to compound ray in the seedling stem is shown in the 
center, in which the compound character of the ray is represented 
in solid black as the ray approaches the periphery of the stem. 
: Conctusions.—The northern oaks in their vegetative axes 
- have the compound type of ray typical of the herbaceous forms. 
On the other hand, the southern oaks have aggregate rays in the 
adult stem, and fossil representatives of the genus are likewise 
characterized by the presence of aggregate rays. The seedling 
and the root of living northern species possess aggregate rays. 
There is no special localization of the reproductive branches in the 
oak as in the amentiferous forms like the birch. This region, 
therefore, which is ordinarily of importance in connection with the 
determination of primitive structure, is of no value here. 
Wounding brings back aggregate rays in the adult axis, and 
in the older seedlings which have begun to form compound rays. 
The results of injury here, as in the birch, must be interpreted 
with reference to the nature and extent of the wound. The 
wound cap of the oak is much smaller than that of the birch, and 
does not so often show hypertrophy to any marked extent. Rever- 
sionary structures accordingly appear on the edge of the wound in 
the wound cap proper, slightly behind the immediate region of 
injury. Oak galls stimulate reversion to an aggregate type of ray 
structure. 
Summary 
1. Experimental investigations are of interest in connection 
with woody plants both from a general biological point of view, 
