244 
C. C. FORSAITH 
those already mentioned in reference to the Betulaceae; i. e., Betida 
populifolia contains normally aggregate rays, while the more advanced 
species, Betula alba, shows them only in primitive localities. 
Considering the Malvales as a whole from the morphological stand- 
point, it is evident that they represent a relatively low order among 
the Dicotyledons, and that the anatomical data appear to assign to 
them a position less high than that designated in the Syllabus der 
Pflanzenfamilien by Engler and Gilg, which places them between 
the Rhamnales and Parietales, both of which have vasicentric paren- 
chyma, a condition very characteristic of the higher Dicotyledons. 
It may be stated here that in the investigations carried on in this 
laboratory, there has never been found a case where vasicentric paren- 
chyma and aggregate rays were coexistent. Therefore, to place a 
group where aggregate rays occur and vasicentric parenchyma is 
characteristically absent, between two orders, which show diffuse rays 
and vasicentric parenchyma, appears to be unjustified. 
There is a striking similarity in the morphological conditions 
found in the Malvales and the lower Dicotyledons in respect to the 
distribution of parenchyma which resembles that seen in Fagus, 
Betula, Alnus, Carpinus, and Corylus (all of which normally present 
diffuse wood parenchyma). In Fagus, however, there is a tendency 
toward a reduction to a terminal position, as mentioned above as an 
analogy to the conditions found in Aristotelia and Elaeocarpus. 
Further, this similarity is no more striking than is that of the ray 
structure, which, as in the above mentioned species, is normally of 
the diffuse type, with a tendency toward a reversion to the aggregate 
condition in Durio, which compares favorably with that found in 
Betula. Investigation has shown that in Betula populifolia, a recog- 
nized primitive species, aggregate rays occur normally, but in Betula 
alba, which is more advanced, such rays occur only in the first annual 
ring, or more persistently in the seedling. 
From the study of the anatomical conditions found in the Malvales, 
it seems probable that they were descended from ancestors .which 
normally possessed diffuse parenchyma and aggregate rays, which 
characters the tropical genus, Durio, still retains in the normal stem, 
and consequently appears from the anatomical standpoint to be the 
most primitive species examined. Without doubt from forms similar 
to this, the other genera were derived. The aggregate ray gave place 
to that of the diffuse type, as a result of the transformation of the 
