OF CBYLOîf AND INDIA. 
423 
most of the secondary shoots, upon short branches, and 
emerge from the water as soon as its level is sufficiently low ; 
by the time that the seeds ripen the thalli are commonly 
quite exposed upon the rock. In Podostemon subulatus the 
process is similar, but the flowers do not open till the water 
falls low enough to expose the tips of the spathes to the air. 
In the other genera the phenomena are more specialized, the 
secondary shoots being reduced and single-flowered. In 
general, all the secondary shoots do not become floriferous. 
In Hydrobryum, Griffithella, andFarmeria, it is usually the 
apical shoots which remain vegetative, and the same is the 
case in most of the Dicræas, but in D.' Wallichii and in some 
forms of D. stylosa, and also at times in Griffithella, scatter- 
ed shoots here and there over the whole thallus remain 
vegetative, while the rest flower. Details must be sought 
under the descriptions of the genera ; the interesting general 
point, and one which {ef. preceding paper, p. 191) has 
important taxonomic bearings, and has in the past led to 
■much error and confusion, is the curious way in which the 
non-floriferous parts of the thalli fall away, leaving the now 
woody flowering portions. 
During the flower development in the forms with reduced 
secondary shoots, the axis elongates, and an interesting 
change of form and function takes place in the leaves which 
are formed at this time (for details see Dicræa, p. 350), their 
sheathing bases enlarging to form bracts, while the filamentous 
assimilating tips finally fall away ; this process also, as 
explained in the preceding paper (p. 193) has led to many 
erroneous conceptions in taxonomic work based on her- 
barium material. Once fully exposed to the air in the 
flowering period, these tips soon fall off, together with any 
not woody parts of the thalli, so that the whole appearance 
of the plant is often changed. This is well illustrated in 
the plates accompanying this paper {e.g., cf. XIV. with XV., 
XIX., 1 and 2, XXXIII. with XXXV., XXXVIII., 6, with 
V., &c.). 
