Boodle.—Anatomy of the Hynienophyllaceae. 463 
structure of the small species of Hyntenophyllum may have 
been derived from the more complex type of structure with 
two xylem-bands, as seen in the larger species. Thus, to 
state the case more fully, a reduction in requirements of 
conducting tissue may very possibly have led to a change in 
structure of the following kind Starting with the structure 
of H. scahrum , for instance, by the abortion of part of the 
lower xylem-band the structure of H. omentum (Fig. 18) would 
be reached; by the total abortion of the lower band the 
structure would be reduced to a curved upper band with 
the protoxylem separated from it by parenchyma: such a type 
is found in H. lineare , Swartz, and apparently also in small 
plants of H. omentum ; finally aggregation of the elements 
of the upper band, and shifting of the protoxylem into contact 
with it, would produce the sub-collateral type of H. tun - 
bridgense. Suppression of the phloem on the lower side of 
the stele would convert the last type into a truly collateral 
structure. This has not been found so far in any species of 
Hyntenophyllum , but it will be described below in the genus 
Triohomanes . Though suppression of the lower phloem does 
not appear to take place in Hyntenophyllum , the upper 
phloem is often much better developed than the lower (see 
Fig. 14), and in more delicate rhizomes the phloem is often 
interrupted at one or more points on the lower side (see 
Figs. 16 and 19), thus showing a tendency to suppression on 
that side. 
The question of the likelihood of the smaller species being 
reduced, rather than primitive, will be discussed below'. 
Another interesting case of diversity of structure in different 
specimens of a species was seen in H. dilatatum . A large 
specimen from New Zealand had an oblong stele in its 
rhizome, in structure like that of the var. Forsterianum (see 
Fig. 9, on the right), while a small plant from Tahiti had 
a much smaller rounded stele, with a small nearly central 
protoxylem-group, accompanied by only a little conjunctive 
parenchyma, and surrounded by the metaxylem, which formed 
a fairly compact mass of tracheides, not clearly separable into 
