OF CEYLON AND INDIA. 
425 
which Warming has named haptera, are questions of some 
difficulty. They are in general formed exogenously from 
the surface tissues of thallus or shoot, while these are young, 
and grow by a growing point rather like that of the roots. 
Not infrequently the apex shows a superficial layer of cells 
like the collenchymatous cap which occurs in most of the 
root-thalli, but very slightly marked, somewhat like that of 
the thallus of Podostemon subulatus. Reaching the sub- 
stratum the haptera flatten out upon it. The flattening, and 
still more commonly a branching of the tip, commonly begin 
before the hapteron has reached the rock. As described in 
detail under Tristicha (p. 295), the hapteron behaves like a 
large root-hair or rather rhizoid. 
Haptera, though exceedingly common, seem only to be 
developed when there is a definite need for their services as 
holdfasts, and it is consequently difficult to determine what 
is their phylogenetic morphological value, or whether indeed 
their occurrence is not another expression of the great 
plasticity of the tissues in these plants. Similar organs are 
common enough in Algæ, Lichens,* &c. Warming and 
Goebel regard them as organs sui generis^ and probably 
this is the best course, though there seems no absolute 
improbability in their being modified adventitious roots, 
which have already gone through the change from endoge- 
nous origin to exogenous, such as seems in progress in the 
thalli of Hydrobryum olivaceum, &c. 
The Spathe and Pedicel, &c. 
The formation of the floral shoot from the vegetative, with 
the interesting change of structure and function in the 
leaves, has been sufficiently described. The interest of the 
floral bracts, spathe, and pedicel is chiefly taxonomic, and 
has been discussed from this point of view on p. 193 of 
the jjföceding paper. It is of particular interest in the 
present connection to point ouc the gradually increasing 
*6/. Sernander in Bot. Notiser, 1901 ; abstr. in Bot. Centr,, 88, 293. 
