SOME FEATURES IN THE ANATOMY OF THE MALVALES 
245 
included fibers to normal ray parenchyma, which, in the other species, 
takes place in the immediate vicinity of the leaf-trace. 
During the gradual transition of the rays to those of a diffuse char- 
acter, there has been, in some cases, a reduction of the wood paren- 
chyma from the uniform diffuse condition, as seen in Durio and Fre- 
montia, to the Hibiscus type, in which there are thin-walled areas in 
which the parenchyma is of infrequent occurrence. This process of 
reduction has reached a higher step in Tilia, where the parenchymatous 
wood elements occur only as tangential bands, with the exception of 
the first annual ring, where there is a reversion to the uniform diffuse 
condition. The climax of this process of reduction is reached in 
Aristotelia and Elaeocarpus, where it occurs only in a terminal posi- 
tion; and, applying the principles illustrated by Salix and Fagus, it is 
evident that these two genera represent the least primitive condition 
since they are the most reduced, and are, therefore, the most advanced, 
of all the Malvales mentioned in this paper. 
Summary and Conclusions. 
1 . The primitive Dicotyledons had apparently diffuse parenchyma 
and aggregate rays. 
2. All the Malvales examined, except Elaeocarpus and Aristotelia, 
show diffuse parenchyma in varying amounts. 
3. Durio presents aggregate rays and diffuse parenchyma, and is 
therefore, to that extent, the most primitive of the Malvales examined. 
4. Elaeocarpus and Aristotelia possess only terminal parenchyma, 
and therefore represent, in this respect, reduced species. 
5. Applying general anatomical principles to the conditions cited 
above, it is evident that the Malvales came from ancestors possessing 
diffuse parenchyma and aggregate rays. 
In conclusion, I wish to express my sincere thanks to Miss Frieda 
Cobb for material of Nothofagus; to the Director of the Harvard 
Botanical Garden for material of the herbaceous forms; and to Pro- 
fessor E. C. Jeffrey for his helpful advice and aid in securing the 
photomicrographs accompanying this article. 
BIBLIOGRAPHY 
1. Jeffrey, E. C, The Comparative Anatomy and Phylogeny of the Coniferales. II. 
The Abietineae. Mem. Bost. Soc. Nat. Hist. 6: 1-37, ph. 1-7. 1904. 
2. Bailey, I. W., The Relation of the Leaf Trace to the Formation of Compound 
Rays in the Lower Dicotyledons. Annals of Botany 25: 225-241, pis. 15-17. 
