DISPERSAL BY BOOT-SHORTENING. 831 



leaf-axils of a few plants had been distributed equally by ploughing over the whole 

 field, although this distribution had certainly not been intended by the ploughman, 

 It would of course be a mistake to explain the uniform distribution of bulbous 

 plants over a large stretch of land exclusively by the ploughing and overturning of 

 clods of soil full of bulb-like offshoots. In many instances the distribution of such 

 offshoots is also produced by the pulling action of the roots. This process is so 

 remarkable that we must describe it somewhat in detail. The multiplication of 

 subterranean bulbs is known to take place by the formation of buds in the axils of the 

 scale-leaves, and these, in the course of a few months, themselves grow up into sniall 

 bulbs. When mature, they may form the termination of a slender shoot which, 

 of course, never attains any considerable length, but which in many cases is thread- 

 Hke, as shown in Muscari racemosum (fig. 444 ^). The small bulbs are pushed by 

 this thread-like shoot out of the region of the protecting scale-leaf near the old 

 bulb, and there they develop long root-fibres in abundance. In other instances the 

 shoots remain extremely short, and the small bulbs are not pushed out, but the 

 protective scale-leaf, in whose axil they originated, decomposes, and they send out 

 their roots through the decomposing tissue into the surrounding soil. In both cases 

 they become detached at the end of the vegetative period in which they originated; 

 they are then no longer connected with the old bulb, but are quite independent. 

 Many species form only one bud in the axil of a bulb-scale, others a whole series 

 which all grow up into bulbs; in the latter case the old bulb in the autumn is 

 surrounded by a whole family of small young bulbs. There is a species of Garlic 

 called Allium pater-familias whose old bulb gives rise to about a hundred young 

 ■ones ia a year. It is impossible for so many to develop properly when closely 

 •crowded together round the plant from which they sprang; mutual pressure would 

 be unavoidable in their further growth, and if next year each of these bulbs should 

 in its turn form new ofl^shoots, and again become the centre of young bulbs, it 

 would become imperatively necessary to make room, and to thin and separate the 

 dense crowd. Since all the bulbs are placed with their apices pointing upwards 

 they cannot be moved apart by the elongation of their stems; the mutual pressure 

 •of neighbouring bulbs as they enlarge would certainly cause a trifling displacement, 

 but this would not prove an efficient remedy. The remarkable pull of the roots, 

 which was described in vol. i. p. 768, now comes into play. Only a few of the roots 

 •arising from the base of a young bulb strike downwards; by far the greater number 

 .grow out at a right angle to the axis of the bulb in a direction parallel with the 

 ■surface of the soil (see fig. 444 ^). When these very long roots have stopped grow- 

 ing they contract, and thus draw the young bulb to which they belong away from 

 the old one. The young bulbs now form a wide open wreath round the old one 

 (which has meanwhile disintegrated), and thus obtain sufiicient room for further 

 development. This happens not only in the Muscari described, but also in 

 Ornithogalum nutans, Tulipa sylvestris, and indeed in quite a number of bulbous 

 plants. Since this process is repeated annually a fairly wide area of soil may in 

 the course of years be covered with the bulbs in spite of the slight distance through 



