22 MR. C. E. JONES ON THE MORPHOLOGY 
Although this distinction appears to be a physiological one, the basis upon which the 
groups are delimited is strictly morphological; in the one case, the vascular eee 
have separated into parallel bands, while in the other differentiation at the meristem 
leads to the formation of more or less isolated areas. In the subgenus Selago, Mr. J i G. 
Baker identifies two groups under the type species Selago and taxifolium. The species in 
each group conform to the same type; but the group of ZL. Selago follows the 
clavatum type, while the group of faxifoliwm, of which most are epiphytie, shows the 
squarrosum type. Practically similar arguments apply to the group of L. inundatum 
and Z. Phlegmaria which are included in the subgenus .Lepidotis. The species of 
L. squarrosum and L. Dathousieanwm are included with L. strictum in the subgenus 
Subselago, which contains species both with erect and pendulous stems. The anatomical 
characters, as I have indicated, would bring Z. strictum close to L. nummularifolium, and 
these and Z. Phlegmaria would be closely allied to Z. squarrosum and L. Dalhousieanum. 
Finally, I should separate L. obscurum very widely from L. cernuum, and the affinities of 
L. alpinum seem to me to lie rather with Z. complanatum than with L. clavatum. In 
making these comparisons, it is not intended to suggest that anatomical structure 
is to be adopted as a basis of classification, except as an aecessory to the more 
important morphologieal features which are usually employed by systematists. 
It may be mentioned here that, in any hypothesis which endeavours to explain the 
dorsiventral structure in the creeping stems, the fact must not be overlooked that the 
banded structure is well marked in the stem of the erect-growing species of L. obscurum 
and the radial structure is maintained in plagiotropie stems of L. cernuum. 
Before adding a summary of the more important results obtained, I desire to state that 
this work was originally begun in the Botanical Laboratory at University College, 
Liverpool, and was continued at the Royal College of Science, London. In addition to 
the help which I have acknowledged in the body of the paper, I wish to express my 
thanks to Dr. D. H. Scott, F.R.S., who supplied me with some of the material used in 
the investigation, and who has always given me most cordially the benefit of his 
assistance and advice. 
SUMMARY. 
1. The development of anatomical structure in 
proceeded along two lines: on the one hand, 
series of alternating bands of xylem and phlo 
is scattered through the mass of xylem in m 
is produced which simulates that found in 
the vascular system of Lycopods has 
as the protoxylems increase in number, a 
em is developed ; on the other, the phloem 
ore or less isolated patches, until a structure 
a Gleichenia. The first form is developed 
in creeping stems, the second is characteristic of tropical epiphytes, and an extreme 
development is found in Z. cernuum and in L. salakense, 
2. The young stem in the seedling shows a triarch or tetrarch structure, in all essentials 
similar to the structure generally associated with roots. 
3. The complex arrangement fou 
tetrarch condition by the divisi 
by the separation of a phloem 
nd in larger stems is developed from this triarch or 
on of one of the protoxylems into two strands, and 
into two portions; subsequently another protoxylem 
ee 
