MORPHOLOGY OF PHYLLOGLOSSUM DRUMMONDII. 
G69 
Where a single leaf is formed first (and this is the case in the large majority of 
specimens) it is usually followed by two of approximately equal size, which are formed 
laterally on the apex of the tuber, and are disposed one on either side of the first 
formed leaf. This is clearly seen to be the case in the specimens represented in 
figs. 11 and 12 (lii.). This pair of leaves may be again followed by a second pair 
(fig. 13, liii.); but here again irregularities of arrangement may, and often do occur: 
thus though in fig. 14 their general arrangement is the same as that above described, 
the leaves do not in this case appear as successive pairs. From the examples cited it 
is evident that there is no strict constancy in number, or arrangement of the leaves ; 
their number is seen to vary from one to five, and the number as seen in the mature 
plant may be occasionally higher still, as many as seven have been seen in one mature 
specimen. It may be again noted that the larger number of leaves is usually 
associated with the absence of sporangia. The arrangement of the leaves also shows 
some inconstancy, there being in the majority of cases one leaf formed first, and 
followed by successive pairs ; in other cases the order of succession and position being 
less regular. In those examples in which the arrangement of the leaves, and their 
order of appearance on the apex are most regular, it is clear that we have to deal 
with a successive ivhorl of leaves. Such successive development of members of a 
whorl is well known to exist in certain flowers, as for example in Reseda , the flowers 
of the Papilionacece, &c. The successive formation of the whorl of leaves derived 
from a node of Chara may also be cited. Further, the irregularities of arrangement 
and succession of the leaves in Plnylloglossum acquire additional interest when it is 
remembered that in the genus Lycopodium irregularities are also prevalent, and have 
always presented difficulties to those who attempt to reduce morphological description 
to strict formulse. The leaves originate on the apex of the tuber as rounded masses 
of meristematic tissue, in which no single apical cdll is to be distinguished; divisions 
of the superficial cells by periclinal walls are frequent, and it is only at a compara¬ 
tively late period that a superficial layer of epidermis becomes apparent. 
Returning now to the central point around which the leaves are disposed, it is at 
no time a prominent cone in those plants which do not form sporangia. According to 
the strength of development of the leaves it is liable to be more or less displaced ; 
this is most clearly seen in those plants in which only one leaf is produced (figs. 8, 9), 
here the apex of the tuber assumes a lateral position at the base of the solitary leaf. 
Even in those cases where the successive whorl of leaves is most complete, the apex 
becomes displaced, owing to the more rapid development of the earlier formed leaves 
(fig. 13). At an early period the apex thus displaced becomes depressed ; it grows 
slowly in length itself, while the tissues immediately surrounding it advance more 
rapidly, the result is a conformation of the surface as seen at («) in figs. 8-14. A 
longitudinal section shows the depression still more clearly (fig. 15). There can be 
little doubt that, in those plants which do not form sporangia, it is actually the apex 
of the plant which becomes thus depressed, since the depression appears constantly in 
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