OF CEYLON AND INDIA. 
413 
In those cases where the primary axis is soon lost, as in 
Dicræa, Hydrobryum, or Farmeria, the mature plant forms 
an interesting parallel to the case of the aquatic Utricula- 
rias;^ the latter are independent ‘‘leaves” of very varied 
form, the former independent “ roots.” 
The formation of secondary shoots upon the roots is of 
course common in other families,! but it is carried to a 
degree of perfection in the Podostemaceæ that is unmatched 
elsewhere. It is clear that we cannot regard the secondary 
shoots of Lawia as homologous with those of the other 
genera, at any rate on the existing evidence, but we may 
fairly regard the secondary shoots which arise upon 
unquestionable root-thalli as homologous with one another, 
though they are.not of course homologous with the primary 
shoots, from which they often differ very largely in structure, 
as well as in position and origin. It is evident, therefore, 
to make a momentary digression, that it is unsafe to draw 
morphological comparisons between the Podostemaceæ and 
other families, using the primary axis of the latter, and only 
the secondaries of the former. 
The secondary shoots of the other genera than Lawia are 
borne upon the root-thalli, endogenously, and are formed near 
the growing apex in alternate acropetal succession. There is 
often a marked tendency for these shoots to be developed in 
pairs opposite to one another, but only rarely is the oppo- 
siteness found to be universal in any particular thallus. 
In Tristicha the secondary shoot is large and complex, 
and ultimately bears many flowers ; we do not yet know in 
what respect, if any, it differs from the primary axis. The 
ramuli, or branches of limited, growth, are a curious feature 
of this genus and its ally W eddellina. In the South American 
Oenones, Moureras, &c., the secondary shoot is large, usually 
with large leaves, is more dorsiventral than in the Tristicheæ, 
and bears the flowers in a large inflorescence. In the 
Eupodostemeæ it is much smaller. In Willisia, to deal 
* Goebel, in Ann. Buitenz., IX. 
t Goebel, Organog’rapMe der Pflanzen, p. 178. 
