464 Boodle.—Anatomy of the Hymenophyllaceae. 
upper and lower bands b This structure, regarded as a reduc¬ 
tion from the type of stele seen in large plants of the species, 
shows a kind of reduction differing from the cases given 
above, and consisting in compacting of the xylem and lessen¬ 
ing of the central parenchyma. As the protoxylem remains 
central, there is no tendency towards the sub-collateral 
type. 
A specimen from Java 1 2 , had a structure very different at 
first sight from that of the specimens just described. It is 
shown (xylem only) in Fig. 21. There appears to be only 
one xylem-band, but as the protoxylem ( px ) is immersed in 
the metaxylem, it does not belong to the sub-collateral type, 
but the tracheides below the protoxylem elements represent 
part of the lower band. It is really similar to the specimen 
from Tahiti, the xylem being compacted, and the reduction of 
intraxylar parenchyma having gone still further ; the chief 
difference being that the xylem forms a band instead of 
a circular mass. H. fiabellatum , Labill, has in its rhizome 
the same type of structure as exhibited by the specimen of 
H. dilatation from Tahiti. Several different-sized plants of 
H. demission were examined, and presented differences in 
the size of the stele, but no departure from the type of 
H. demissum , var. nitens , except in the case of a small sterile 
specimen from Otago 3 , where the lower band was missing, 
and the structure was therefore as in H. lineare. 
It must be pointed out that equally marked differences in 
structure might occur in others of the species described above. 
Thus in H. lineare , where only one specimen was examined, 
a larger plant might possibly have had a lower xylem-band, 
or a smaller plant might have shown typical sub-collateral 
structure. 
1 This shows an approach on a small scale to the structure of Trichomanes 
radicans , as will be seen by referring to the description of the latter. 
2 Collected by Raciborski and identified as H. Junghuhnii , Bosch., which is 
.regarded by Hooker and Baker (Synopsis Filicum, p. 62) as a synonym of 
//. dilatatum. 
3 Mr. J. G. Baker kindly gave me his opinion that this specimen was correctly 
named. 
