818 THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



Antilles, and above the disc-shaped bracts on the top of the stalk on a considerable 

 number of species of Allium (e.g. Alliwm Moly, vineale, oleraceum, carinatum, 

 arenariuTn, Scorodoprasum, sativum). A second type, growing in the axils of bracts 

 on the upper part of the stem, is shown by Polygonum bulbiferum and viviparum, 

 natives of the far north, and of the Alpine regions of Europe and the Himalayas (see 

 figs. 452 1' ^' 3. *. 5, 6, 7, 8^_ These are not bulb-like structures, but small tubers or corms 

 with a minute terminal bud projecting like a little horn, and the tissue of the tuber 

 is abundantly filled with starch and other reserve materials (see figs. 452^ and 452^°). 

 The third type is observed in species of the genus Olobha, belonging to the 

 Scitaminese, more especially in the East Indian Globba bulbifera and in Olobba 

 coccinea, which grows in Borneo. These rare plants develop offshoots in the axils 

 of bracts on the uppermost part of the rigid stem. They consist of a small bud, 

 from whose minute axis a thick, fleshy root filled with reserve materials grows 

 down, so that in reality the chief part of the offshoot consists of a root-structure. 



When the closed bulb-like offshoots, tubers, or buds with thickened roots have 

 been thrown from the wind-swayed stem they remain unaltered in the spot where 

 they have found a resting-place through the whole winter, or the whole dry period 

 of summer. At length, when the most suitable time of year arrives, little 

 absorbent roots make their appearance (see fig. 452 ^) at the expense of the stored- 

 up reserve materials, and these fix the offshoots in the soil and convey fluid 

 nourishment to them. The axis of the offshoot elongates and grows into a stem, 

 putting out leaves and forming a new independent plant. 



The entire sprouts, which are detached from aerial stems and become offshoots, 

 can obviously not be transported very far by wind. They are much too heavy, and 

 offer no suitable hold to the wind, which can only influence them by shaking the 

 stem on which they are supported, or by rolling them along after they have fallen 

 to the ground. In the former case the sprout-like offshoots are jerked off", and the 

 action of the wind is therefore only indirect. Some plants bear side by side on the 

 same stem tubers with undeveloped buds, and also some whose buds have begun to 

 grow into sprouts, and have developed green foliage-leaves. These form a connect- 

 ing-link between the groups just described and those we are now about to consider. 

 One of them is the already mentioned viviparous Polygonum, (Polygonum viviparum, 

 fig. 452), in which it often happens that all possible stages of development occur 

 close together on a single spike. 



In Grasses especially it is often the case that the offshoots when ready to be 

 detached have the form of developed, leafy sprouts. In the Grasses of the Arctic 

 flora belonging to the genera Poa, Festuca, and Aira, the formation of leafy sprouts 

 which become offshoots is so usual that in places the plants bearing offshoots are 

 more common than those bearing flowers in their panicles. On our high mountains 

 also there grows a grass (Poa alpina, cf. fig. 342 ^, p. 455), in which the panicles as 

 often bear offshoots as flowers. On the plains of Hungary flourishes a species of 

 Meadow-grass (Poa bulbosa), in which the same thing happens to such an extent 

 that in the many thousand plants which cover the ground all the panicles develop 



