aquilimim , with some Notes on Marsilia quadrifolia, cfc. 581 
within each sieve tube, and necessarily works outward in all directions 
towards the middle lamella, would hardly be supported by the facts in 
Pteridium. Of course it may be that callus does occur very transiently 
in these pits at some stage, examples of which have not been hit upon. 
This seems hardly probable, as, did it occur, the most likely place would be 
in sieve tubes where the sieve plates show the presence of callus ; but in 
these no callus was found in the pits in question. If the slime strings 
become bored out by use, by the travelling of ferments and other sub- 
stances along them, it seems strange that the same process should not 
take place in the case of threads leading into the phloem parenchyma cells, 
which have every appearance of being in a state of activity. 
Accumulations of callus (PI. LIV, Figs. 10 and 11) were occasionally 
observed, but their presence could not be connected with any particular 
stage in development, nor was their distribution at all regular ; possibly 
their formation is attributable to some pathological condition in the particular 
elements in which they were found. Callus formation is generally entirely 
limited to the paired basins connected with each slime string. Material 
was gathered in December and examined for accumulations of callus, block- 
ing the sieve tubes during the winter rest, but no evidence of anything 
of the kind could be seen. Sections were examined, from the apex of the 
rhizome backwards to regions as much as five years old (the giving off 
of a frond being taken as an annual event), and in no part was a develop- 
ment of callus beyond the ordinary detected. It does not seem therefore as 
if any blocking of the sieve tubes during winter takes place. 
Marsilia quadrifolia. 
No systematic examination of Marsilia was made, as has been stated 
already, but the stage at which callus is developed was detected, and every- 
thing indicated that the mucilaginous droplets behave in the same way as in 
Pteridium . The lateral plates in the internodes are few and small, often 
taking the form of isolated threads in pits ; they seem to be but little used, 
as even in sections of comparatively older material their threads appear to 
be granular, protoplasmic, and unaffected by ferments. 
Some material of Lygodium dichotomum was also examined, especially 
in order to investigate the presence or absence of callus, in view of Boodle’s 
inability to demonstrate it in the Schizaeaceae 1 None could be detected, 
but, as the material available was all of nearly the same age, this was not 
surprising. Preparations stained with safranin were not made, so that 
no definite statements can be made as to the perforation of the sieve plates, 
but the aspect of the unstained sieve tubes suggested that they did not differ 
materially from those of Marsilia and Pteridium. 
1 Boodle (’ 01 ), p. 396. 
Q q 
