BOTANY. 



577 



position, place and duration. It appears as a tuber 

 a bulb, a scape, a culm, or as a woody column. It 

 varies in size from that of a bristle to a trunk of 

 many feet in diameter. In structure, stems are 

 hollow or solid, jointed or simple, single or numerous. 

 In position they are erect, inclining, prostrate or in- 

 volving. They rise in the air, creep on the surface, 

 or enter deep into the ground. They are succulent 

 or woody : if the former, they are quickly perishable, 

 if the latter, they are more or less durable. 



Tuberous stems are exemplified in the iris and 

 potato. The first is a stem, branched or single, 

 partly beneath the surface of the ground, from 

 which the real roots are ejected ; and partly above 

 the ground, the top bearing the leaves and flower 

 stem. The second is a plant which, whether propa- 

 gated from seeds or cuttings, has a system of fibrous 

 roots on which the whole depends for support. The 

 plant produces stems of two descriptions, one in the 

 air which bears the foliage, flowers, and fruit : others 

 in the ground, which, when they have shot a few 

 inches from the root, instead of being lengthened out, 

 stop the point swells, and becomes a tuber of a 

 larger or smaller size, according to the richness of the 

 soil, or variety cultivated. When the seeds are ripe 

 the whole plant dies, leaving the oviparous progeny 

 perfected in the air, and viviparous offspring matured 

 in the earth, to perpetuate the species. The tuber 

 has a large farinaceous pith, covered with a thick 

 coat of the like substance, and a thin exterior cuticle. 

 Those integuments are studded with groups of buds 

 or eyes, independent of each other, over the whole 

 surface, and particularly at the point or crown. Each 

 of these groups, when dissevered with a portion of 

 tuber attached, become perfect plants, and again in 

 their turn produce other seeds and tubers. A plant 

 with such powers of reproduction, and in its native 

 climate, must soon usurp the surface of the surround- 

 ing country, did not their numbers, by diminishing 

 and robbing each other, confine them to very limited 

 spaces. 



There are many other plants similarly constituted, 

 that is, such as produce stems in the ground, as well 

 as in the air. Of these may be mentioned the Jeru- 

 salem artichoke (Hefianthus Inbcrosus}; the field 

 bindweed (Convolvulus arvensis'); the couch grass 

 (Agropyrum repcns), &c. There are also aquatic 

 plants, the principal stems of which are extended in 

 the mud, as the water lily (Nymphea). 



It is worthy of remark here, that plants which have 

 the property of increasing themselves by both seeds 

 and offsets, produce the one in greater abundance, 

 where means have been taken to prevent an increase 

 in the other. Thus for instance, the potato denied 

 its purpose of producing seeds by being deprived of 

 its flowers, the tubers in the ground will be much 

 increased, as well in size as in numbers. On the 

 other hand, if the young tubers be removed from the 

 plant as soon as they are formed, and none allowed to 

 be perfected, the numbers of flowers and seed will be 

 greatly increased. So rare or curious bulbs, which 

 yield flowers, but do not ripen seeds in a climate 

 foreign to them, may be forced to produce offsets 

 by denying them the means of flowering, that is, 

 by cutting oft' the upper half of the bulb. The same 

 law of nature is exemplified in the English elm, 

 which in this country bears no seeds ; but to com- 

 pensate for this defect, produces annually abundance 

 of snckers. 



NAT. HIST. VOL. I. 



A bulbous stem has the collet for a base whence 

 the roots are produced ; on the upper disk of the 

 collet the leaves are seated involving each other 

 round the centre, the exterior ones incrassated, ab- 

 breviated, and remaining for a longer or shorter 

 period of time as a defence to the fructification before 

 its expansion. The roots, leaves, stalk, flower and 

 seed produced in this year are all deciduous, and fall 

 off to be succeeded by the next division of the sys- 

 tem, which will be developed in the next. As an 

 example we may take the tulip, figured beneath. 



Section of a tulip bulb in autumn a, the flower of the follow. 

 ing spring ; l>, the succeeding division of the bulb which is per- 

 fected during the summer. 



In other bulbs, as the hyacinth, polyanthus 

 narcissus, there are always two or more divisions of 

 the bulb coming forward together in different stages 

 of their progress towards flowering : consequently 

 these bulbs are always larger than those of tulips, or 

 others of more simple character 



There are many modifications of this kind of stem. 

 Some are very slightly bulbous, as the leek and blue 

 African lily ; others much expanded, as the Spanish 

 onion and some of the Cape bulbs. The thick gouty 

 stems of the crinum and aletris appear to be only the 

 remaining bases of former leaves. 



The internal structure of the bulbous stems is 

 different, according as the leaves of the plant are 

 placed with regard to each other. This may be 

 rendered evident, by making a transverse section 

 of the bulb : the outermost leaf partly or wholly 

 embraces all the innermost, one of the edges over- 

 lapping the other, but without adhering, as in the 

 leek ; the onion having fistular leaves the coats of 

 the bulbs are entire. This description of bulb is 

 said to be coated (tunicatus). Another difference of 

 structure is exemplified in the common white lily 

 and other liliaceous plants ; the exterior of the 

 bulbous body being composed of thick fleshy scales 

 attached to the radical plate : hence these are 

 called scaly bulbs (Squamosus). A solid bulb has 

 also been described in old books, and the tulip has 

 been pointed to as an example, but this is an error : 

 the tulip is a coated bulb ; nor has there been any 

 bulb of that description yet discovered. 



A scape is a stem which springs immediately from 

 the radical plate of a bulb, as the daffodil, or from the 

 crown of a herb, as the primrose. 



A culm is a hollow stem, cither jointed, as most of 

 the grasses, or simple, as some of the rushes. 



The above enumerated stems are mostly succulent, 

 and either hollow, or filled with a soft cellular pith, 

 the exterior being formed of a fibrous cylinder, 

 charged with parenchymous and vascular tissue, and 

 covered with a thin transparent cuticle. The greater 

 number rise erectly in the air or water ; some creep 

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