402 BOTANICAL GAZETTE [DECEMBER 
characterized by palingenetically large leaves and dorsal or abaxial 
sporangia are in reality so united by a common plexus of origin that 
they may be with advantage mustered under a common appelation. 
Although the standing of the Pteropsida as a large natural 
phylum of plants now appears to be on a firm footing, the important 
question of the morphology of the central cylinder or stele of 
vascular plants is still the subject of much controversy, and the 
English school of morphologists, led by Dr. D. H. Scorr, who is 
himself a host, has attacked the present writer’s position with 
great vigor. The Pteropsida certainly are the appropriate battle 
ground for the decision of the fundamental morphological ques- 
tion of the internal morphology of the stem, since, unlike the 
Lycopsida, they are still in full vigor, while they share with the 
latter phylum the advantage of a very extended history. The most 
important line of attack is in connection with the morphological 
status of the pith, which the present writer regards as external 
tissue included by the stele in the course of evolution. The 
English anatomists, on the contrary, regard the pith as in all 
cases a specially differentiated central portion of the fibrovascular 
tissue itself. Of late, however, the extremity of the English view 
appears to be modified somewhat by the admission that in certain 
instances the pith may be derived from outside the stele. Another 
less important and not generally adopted criticism of the author’s 
views is to the effect that the megaphyllous or large-leaved habit 
is not a primitive one for the Pteropsida. This criticism has been 
put forward by only a few of the English anatomists, and appears 
to have been effectually answered by two recent American writers 
on the subject. 
The lapse of time has made the task of replying to criticisms 
against the extrastelar origin of the pith a much easier one. € 
growing-point hypothesis, which has been applied by STRAS- 
BURGER to the elucidation of the morphology of the pith, has been 
recently rejected by a number of morphologists in Europe and 
America? The interpretation of the mature structure of the organs 
? JerrrEy, E. C., Morphology and phylogeny. Science N.S. 23+:291- 1906. 
Bower, F. O., The origin of a land flora, chaps. xiv and xv. London. 1908- 
Courter, J. M., Vascular anatomy and the reproductive structures. Amer. 
Nat. 43:219-230. 1909. ~ : 
