160 BRITISH PLANTS 
weak stems. Some of the leaves bear tuberous buds 
(bulbils) in their axils, but they have the same struc- 
ture as the underground tubers. Subterranean leafy 
bulbils are found in Saxifraga granulata (the meadow- — 
saxifrage), and these form the chief means of propa- 
gation. i 
5. Aerial Bulbils.—These are fleshy brood-buds which 
arise on aerial stems. They become detached, fall to the 
ground, root, and grow into new plants. In the tiger-lily 
they develop in the axils of the lower leaves, and when 
the plant dies they separate. In some species of onion— 
e.g., Allium vineale—they replace some or all of the 
flowers. In very wet places, such 
as water-meadows, it is rare to find 
any flowers at all on the plant. In 
drier places, where the chances 
against the survival of the bulbils 
are increased, flowers are produced 
instead. 
6. Viviparous Plants.—New plants 
sometimes appear on the most un- 
likely parts of plants, and almost 
any organ may, if the proper stimu- 
lation is present, become the seat 
of vegetative budding. Thus the 
Fre. 64.—Raprcar Lear leaves of Begonia become viviparous 
or Cuckoo-Fiowzr (Latin vivus, alive ; pario, I produce) 
(Cardamine pratensis), if they are pegged to the ground and 
SHOWING FORMATION their veins slit across. Buds are 
or NEW PLANTLET ON ane 
Termina, Lxearter, formed adventitiously at the lower 
(ArTER KERNER.) ends of the severed veins. From 
these buds little plants arise, which, 
if separated, take root easily in the soil and grow. 
Similar plantlets are formed on the radical leaves of 
the cuckoo-flower (Cardamine pratensis) when growing 
in wet, fertile meadows (Fig. 64). In many alpine grasses 
—e.g., Poa alpina and Festuca ovina—the flowers become 
transformed into plantlets (Fig. 65). The stimulation in 
all these cases is produced by the accumulation of excess of 
nutritive material at certain points. In the Begonia the 
retreat of the sap down the leaf is stopped at the points 
where the veins are severed and the buds arise. In the 
alpine grasses flowers are not produced because of the 
