46o THE BIOLOGY OF FLOWERING PLANTS 



may be very long. The span of life, which in some cases 

 seems so very definite, may be easily modified. Where the 

 span is longer, as in trees, it also seems to be less definite. 

 Its investigation is difficult, for the tree so often outlives 

 many generations of men ; a Sequoia has been felled during 

 the present century which was a seedHng about 1317B.C., 

 over 3000 years ago (Douglas, 191 9). In the case of 

 herbaceous, bulbous, and aquatic perennials we meet with 

 another difficulty in determining the length of life. 



Vegetation Multiplication. — Most perennials multiply 

 vegetatively. In a creeping plant like the ground ivy the 

 ordinary stems root at the nodes, and may ultimately 

 become separated from the parent. Underground rhizomes, 

 as in the wood anemone, or rootstocks, as in the primrose, 

 branch and, by the dying off" of the old parts, give rise to new 

 plants. The strawberry sends out special runners, axillary 

 shoots with very long internodes producing one or more 

 rosettes of leaves, which root and become separated from the 

 parent and from each other. Runners of a simpler type 

 are produced by the bugle and willow herbs. Axillary 

 subterranean shoots in the potato or artichoke form swollen, 

 food-storing tubers, which separate on the death of the 

 parent. In bulbs and corms axillary buds grow into 

 daughter bulbs and corms which replace or multiply the 

 old. Many shrubs and trees form suckers, as the rose and 

 willow ; trailing branches take root as in the Rhododendron, 

 and bramble. Buds may also arise on the roots, as in the 

 sheep's sorrel and the elm, the roots of which, after a tree 

 has been felled, may send up shoots many yards distant 

 from the parent trunk. Adventitious buds may be formed 

 on leaves and take root, as in Cardamine pratensis. Begonia, 

 Tolmeia, or the famous Bryophyllum calycimim. Finally 

 we may mention the so-called " viviparous " production 

 of bulbils, or shoots, in place of seeds by varieties of Poa 

 alpina, Festuca ovina, Polygonum alpinum, by Cardamine 

 bulbiferay and by many other plants, which Ernst (19 18) 

 regards as an expression of hybrid vigour. The possibilities 

 of vegetative propagation have been taken advantage of, 



