448 MR. G. BREBNER ON THE 
Marattia attenuata show certain differences in this respect, and 
will be dealt with separately. 
The development of the caval, even when pursuing a longi- 
tudinal course, is not strictly acropetal, as the schizogenous 
space may vary irregularly in width at different levels in the same 
developing canal. In the petioles and rachides, especially of the 
second and third order, where the canals pursue a pretty straight 
course, they taper fairly uniformly towards the apex except 
where disturbed by a lateral anastomosis. Further, the separate 
canals are frequently at very different stages of development at 
the same level. For example, in the case of a very young leaflet 
of Marattia cicutefolia, in which there were three canals in the 
parenchyma of the mid-rib, the solitary canal on the upper side 
of the bundles was much wider than either of the two in the 
parenchyma on the under side and was longer in dying out. 
Moreover, a certain amount of basipetal development may be 
presumed to take place in certain cases, as in the tertiary 
pulvinus, or pulvinoid thickening at the base of a leaflet, the 
canals die out in the downward direction, tapering towards their 
proximal end. This would be accounted for if the parenchyma 
of the pulvinus remained longer meristematic than in the rest of 
the frond, of which there is indeed some sign. 
True mucilage-canals, although obviously present in the stem 
and fronds of Angiopteris evecta (var. hypoleuca?), were not 
found in the roots, aerial or other, nor in the aerial roots of the 
type species. In these there were only elements, both isolated and 
in rows, which gave the tannin reaction with iron (blue), con- 
firmed by the bichromate of potassium test. Such of the tannin- 
sacs as form longitudinal rows frequently seem to have an 
epithelium, especially seen in transverse section. Study of 
developmental stages, however, clearly showed that the appear- 
ance was simply due to the pressure of the contents of the 
tanniferous cells on the surrounding parenchyma; but even in 
the adult condition this pseudo-epithelium is very different in 
appearance from that of the true canals. The appearances 
presented by these tannin-sacs in their early stages are exceed- 
ingly like what Kiihn has described and figured as illustrating 
the “lysigenous” development of the mucilage-canals, but they 
are not at all like the early stages in the development of the true 
canals as described above. 
In the aerial roots of Angiopteris evecta, var. pruinosa and 
var. Teysmaniana, there are mucilage-cavities which form a well- 
