231 
Compound Rays in the Lower Dicotyledons . 
the first few years’ growth, but during subsequent growth the quantity of 
parenchymatous storage tissue related to the leaf-trace is constantly 
increased until it extends a considerable distance below it. Fig. 28 illus- 
trates the former condition ; the associated compounding dies out a short 
distance below the leaf-trace. Fig. 30 illustrates the leaf-trace at some 
distance from the pith ; a long aggregate ray, a small portion of which can 
be seen in the figure, now subtends the leaf-trace. In transverse sections, 
as may be seen in Fig. 26, the aggregate rays appear to originate at some 
distance from the centre of the stem, and only in sections cut in the 
immediate neighbourhood of the leaf-trace does the aggregate ray extend 
to the vicinity of the pith. The condition, which exists in the primitive 
Live Oak, indicates that, in all probability, with the development of unequal 
seasonal temperature and rainfall, parenchymatous storage tissue has been 
increasingly developed in the vicinity of the leaf-trace. This tissue has 
subsequently been increased in amount until highly specialized sheets of 
storage tissue or aggregate rays result in the mature portions of the plant. 
As might be expected, American oaks with deciduous foliage possess 
higher stages of the development of storage tissue in relation to the leaf- 
traces. In seedling White Oaks, according to the law of recapitulation, 
a condition similar to that of the mature Live Oak stem exists. There is 
this difference, however, that although the rays do not extend to the pith 
above and below the leaf-trace, they pass through the stages of compounding 
abruptly, the phase of compounding being confined to one or two annual 
rings. In the mature stem of this sub-genus the lateral leaf-trace rays 
become gradually more firmly seated upon the plant, and originate in their 
internodal extensions in the vicinity of the pith. Fig. 25 illustrates the 
cross-section of a small twig of Quercus alba , L. It will be noted that there 
exists in oak a five-lobed pith. At each node a median trace passes off 
from the extremity of one lobe, and two lateral traces from the sides of the 
adjoining lobes. As more or less persistent aggregate rays are associated 
with the lateral traces, a section of the stem possesses usually ten aggregate 
rays which are grouped in pairs. Occasionally, however, aggregate rays 
develop in relation to the median traces, or one or more of the lateral 
traces may be abortive, in which case an odd number of compound rays 
exists in the cross-section, as is the case in Fig. 25. In the Red Oaks the 
aggregate rays are more firmly established upon the plant than is the case 
in the White Oaks. Thus, in seedling Red Oaks, as in the mature twigs of 
White Oaks, the associated tissue above and below the leaf-traces extends to 
the neighbourhood of the pith in the internode, as well as to the point at 
which the trace passes to the leaf. In mature twigs of Red Oak, as may be 
seen in Fig. 27, a transverse section of Quercus velutina , the tendency for 
the formation of aggregate or compound rays has become so firmly fixed 
upon the meristematic tissues that numerous rays, in addition to the charac- 
