STOLONS AND BULBS. 59 



{Siackjis, Men/ha). With these forms are connected those in which the end of a 

 subterranean runner does not develope into a sub-agrial leaf shoot at once and 

 in the same period of vegetation, but swells up as a thick tuber, on which, in 

 the axils of very small arrested leaflets, buds (eyes) are situated, from which rooted 

 sub-ae'rial leafy shoots arise in the next period of vegetation : from these again 

 arise tuber-producing subterranean runners. We find an example of this, as 

 well known as instructive, in the Potato, 

 and the Jerusalem artichoke {Helianihus 

 tuberosui). 



Many bulbs also arise at the end of 

 subterranean runners," e. g. those in young 

 tulip plants. Bulbs are distinguished from 

 tubers, however, in that, in them, not 

 the shoot-axis, but the leaves envelop- 

 ing the leaf-bud become thick, succulent, 

 and fleshy, and filled with reserve mate- 

 rials like the tubers. In the majority of 

 bulbs, however, the buds arising in the 

 axils of the bulb-scales are transformed 

 at once into new bulbs, which are 

 not removed by far-reaching runners 

 from the parent bulb. This is the case, 

 for example, in our common kitchen 

 Onion, the Garlic, Crown Imperial, and 

 many others. It is evidently an advanta- 

 geous arrangement when tubers and bulbs, 

 from which new plants arise in the next 

 year, are formed at the end of more 

 or less long runners ; since the newly 

 arising individuals are thus developed far 

 from the mother-plant, in a soil which has 

 not yet been exhausted by the latter. 



It is clear that all plants with run- 

 ners (above ground or below, forming 

 tubers and bulbs or simply bearing leaf- 

 shoots at the end) are constantly travelling, 

 and consequently they appear each year 

 in places further distant. If such plants 

 are particularly well adapted for the soil 

 and prevailing climate, they may at length 



completely occupy wide stretches of ground, since they dispossess all other plants. 

 Such is the case with the Couch Grass (Trilicum repens) and with many Sedges 

 {Carex), and particularly with the Horsetails (Equiseturri) : Equisetum limosum, 

 and paluslre, for example, are able, by means of their subterranean runners creeping 

 in the mud, to occupy large stretches in bogs and the margins of ponds and lakes, 

 to the exclusion of other plants. Plants provided with subterranean runners play an 



Fig. 54. — Longritudinal section through a germinating bulb 

 of Tulipa pracax. k brown membrane covering the bulb ; k 

 the part of the stem bearing the bulb-scales {sh, jA) ; si the 

 elongated portion of stem bearing the foliage leaves {i' V) 

 which ends above in the terminal flower ; c ovary ; a anthers ; 

 p perianth ; 2 a lateral bud (young bulb) in the axil of the 

 youngest bulb-scale ; A the apex of the first leaf of this lateral 

 bud. The lateral bud developes as the bulb of next year, w 

 the roots which arise on the fibro-vascular bundles of the base 

 of the bulb. 



