322 WILLIS ; MORPHOLOGY OP THE PODOSTEMACEÆ 
The length of the pedicel of the fruit is very variable, 
especially in the more northern forms ; I have found 
pedicels from 6 to 25 mm. long on one plant. What deter- 
mines the length I cannot say, but incline to think that it 
is partly the rate of fall of the water-level, this again partly 
depending on slope of rock, &c. In determining varietal 
distinctions, the average length of a large number of fruit 
stalks should be taken. A half- ripe fruit also may ripen 
after gathering without lengthening its stalk. 
Rejuvenescence , — One of the most important features in 
the general life-history of this, as of other species of the 
order, is its almost infinite capacity for rejuvenescence of 
its thallus from any part thereof which remains alive. So 
long as any portion, however small, of the thallus is alive, it 
seems capable, if submerged in favourable conditions, of 
forming anew growing point and re-commencing its growth. 
The new apex forms near the edge of the old or damaged 
portion of thallus, and begins at once to grow outwards 
horizontally, showing the same structure and development 
as the growing points previously described. An example 
of such a new growing point is shown in PI. XI., fig. 8. The 
importance of this capacity to the plant is very great. The 
ordinary growing points soon die if exposed to air by the 
fall of the water, and are also liable to damage from larvæ 
of insects and in other ways. The damage to the plant is, 
however, only temporary, as new apices are at once formed 
and the growth goes on again. It is largely owing to the 
extensive formation of these secondary growing points that 
the morphology of the mature thallus is so complex and 
difficult to unravel. The secondary growing apices may form 
flowers, just like the primary ones. 
Owing to this capacity for rejuvenescence, the plant can 
hardly be called strictly annual. As the water falls in the 
dry season, the bulk of the plant, or all of it in some cases 
if the fall be very rapid or the rock horizontal, becomes 
exposed to the air, and if it so remain for more than perhaps 
a week or ten days, it often or usually dies, having in the 
