FLORA OF TIBET OR HIGH ASIA. 223 
or propagation may be effected; namely, by seed and by vegetative 
increase. It has already been explained that few of the Tibetan 
plants are annual or monocarpic, and that most of those species 
which are, are exceedingly rare and only met with as solitary 
individuals. It is possible, however, that individuals are much 
more numerous in some years than in others. With regard to 
the production and maturation of seed, there seems no reason 
why every species or almost every species in the Flora should not 
do so, as it seems to be quite independent of altitude. About 
twenty-five per cent. of the species are represented by dried 
specimens bearing ripe fruits and seeds, and these species comprise 
members of almost every natural order in the Flora. Many of 
those not represented by fruiting specimens were collected too 
early in the season to secure fruit. Some of the plants produce 
seeds very copiously, and, given the conditions favourable to 
germination and subsequent growth, there ought to be an 
increasing vegetation; but the perennial drought, the shifting 
sands, and the large herds of herbivorous animals, conjointly, are 
probably sufficient to prevent the spread of most plants. Among 
the plants which undoubtedly increase vegetatively are the 
species of Allium, from bulbs; the cushion-like plants, by 
successive branchings or offsets; and the trailing plants, by 
runners or rooting of the new branches. Doubtless most of the 
grasses increase in this way, but perhaps only enough to make 
good the previous season’s consumption. But under any circum- 
stances and conditions the spread of plants vegetatively in 
Tibet must be a very slow process, because none of them, so far 
as we know, produce runners or rooting branches of great 
length. 
The dispersal of the seeds and fruits of plants by wind and 
other agencies in Tibet is certainly much greater than the pro- 
babilities of successful germination in the localities to which they 
are transported. It is a significant fact, however, that the 
achenes of Saussurea, one of the commonest and most widely 
spread genera, have a plumose pappus, and might be carried 
almost any distance and height by the prevailing winds. Further, 
there is not a seed produced in Tibet which might not be con- 
veyed in the great sand-storms; but the chances of their meeting 
with favourable conditions must be very remote. The few 
berry-bearing plants, such as Ephedra, Hippophaé, and Nitraria, 
have an equally small chance of being successfully dispersed by 
