Notes . 
173 
arise from adventitious buds upon old parts of the rhizome. Possibly 
Helminthostachys or its ancestors branched more copiously, and 
Farmer’s adventitious buds are due to the fact that this latent capa- 
bility may still be stimulated into action under certain conditions. 
The fact that these buds are most frequently found upon almost decor- 
ticated fragments of rhizome appears to give colour to this suggestion. 
It may also be suggested that they represent glandular organs of 
some kind ; but, at the present day, the cells surrounding them give 
no particular evidence of a glandular nature. 
D. T. GWYNNE-YAUGHAN. 
Glasgow. 
ON SECONDARY THICKENING IN AN GTOPTERIS 
EVECTA. — For some time past Professor Farmer and the writer 
have been engaged upon an investigation into the structure of certain 
Marattiaceae. Various interesting features have come to light, amongst 
which is secondary thickening in Angiopteris evecta. 
As is well known the steles of this plant are concentric in structure, 
the xylem being surrounded by the phloem. Both these tissues are 
arranged in an irregular manner, and between them there may often 
be seen elements exhibiting a marked radial arrangement, exactly 
presenting the appearance usually associated with that of a cambium. 
This cambium does not by any means surround the xylem, but is of 
local occurrence. There can be no doubt that the tissue in question 
owes its presence to post-embryonic merismatic activity, in fact to the 
existence of a cambium, though restricted to localized areas. 
Additional evidence is afforded by the fact that on the inner side 
of this tissue semi-lignified elements with protoplasmic contents are 
often formed. 
The only other view that could be held regarding this formative 
tissue is that its occurrence is due to the retention of the arrangement 
of primary meristem. It is, however, extremely doubtful if such a 
tissue would retain its characteristics for so long a time, for the best 
cases of secondary tracheides, accompanied by a cambium, were seen 
in the lower and older regions of the plants. 
Secondarily formed tracheides have also been seen in the petioles, 
but not in the roots. 
It may also be mentioned that outside the stele there is evidence 
of a tentative cambial activity. The latter is again irregular in its 
