378 BOTANICAL GAZETTE [NOVEMBER 
Figs. 7-10 illustrate the normal and traumatic wood of the well 
known Quercus alba, a deciduous oak with highly specialized ray 
structure. Figs. 8 and ro, tangential and transverse sections respec- 
tively of the traumatic wood, show that this species also reverts 
to ancestral type of ray structures. 
This reversion to ancestral conditions has been found by the 
writer in woody tissues subsequent to severe injury. Slight 
injuries, on the other hand, particularly in oaks with highly special- 
ized ray structure, often produce no morphological effect upon the 
wood. In a limited number of cases very slight wounds have 
produced a stimulation of the compounding tendency or accelera- 
tion of development rather than a reversion to ancestral structures. 
In fig. 11 may be seen a cross-section of Alnus sp. The lower 
portion of the figure shows none of the so-called false rays, but 
in the upper half numerous rays have developed abruptly outside 
a zone indicating slight injury. Fig. 12 shows a similar phenome- 
non in the young stem of Quercus densiflora. In the lower half 
may be seen normal seedling wood in which only uniseriate rays 
occur. Starting from a zone of slight injury in the middle of the 
section, a compound ray has suddenly appeared in the upper 
portion of the figure. From this we see that very slight injuries 
produce an acceleration in the formation of compound rays. 
SUMMARY AND CONCLUSIONS 
1. The phylogenetic importance of traumatic areas as the seat 
of reversion to primitive structures is well illustrated by the spect- 
mens of wounded oak wood which have been examined by the 
writer. 
2. In traumatic wood progressive stages are found which are 
similar to the stages of recapitulation found’in the seedling, and 
equivalents to the condition found in adult miocene oaks. 
3. Woody tissues in the immediate vicinity of a severe wound 
show only non-aggregated uniseriate or small rays. In subse- 
quently formed tissues the gradual building up of the compound 
ray may be traced in a consecutive series of steps to the normal 
homogeneous large ray of the adult wood. 
4. On the basis of traumatic and developmental as well as paleo- 
