INTRODUCTION 
surface, whilst it bears but few roots. It is, moreover, generally a 
swollen branch or secondary, rather than a primary, stem. The rounded 
or hand-like ( palmate ) structures generally borne by our Orchids and 
often called tubers are mainly of root origin and have only a terminal bud. 
They are, therefore, preferably distinguished as root-tubers or tubercles. 
The bulb , though resembling a corm externally, is a short conical 
stem of many internodes, giving off adventitious roots below, but 
enclosed above in a mass of overlapping fleshy leaf-scales, so that it is 
in fact a persistent bud. When these leaf-scales are broad so as to 
wrap round most of the circumference of the short stem, as in an Onion, 
the bulb is called tunicate ; but when they are narrow so as merely 
to overlap like the tiles of a house, as in a Lily, it is termed scaly , 
squamose , or imbricate (Latin squama , a scale ; imbrex, a tile). Buds originate 
in the axils of some of the scales and develop into fresh bulbs, known 
w hen young as cloves , and these become afterwards detached and thus 
multiply the plant. 
Another method of vegetative reproduction is the formation of 
suckers , which are branches given off by a stem underground, and, 
after growing for some distance horizontally, rising above ground into 
leafy shoots and becoming capable of independent life by sending out 
roots from their lower parts, thbs differing from runners chiefly in 
being partly subterranean. Many members of the Rose Family, such 
as the Raspberry, the Rose, and the Strawberry possess one or other 
of these methods of multiplication. 
The aerial stems of plants, i.e. those developed above ground, may 
be annual or perennial in duration, branched or unbranched, woody or 
herbaceous. If the main stem dies within the year from the sprouting 
of the seed, the plant is an annual ; but if it is only secondary branches 
that die down to the ground in autumn, leaving an underground stem 
to prolong the life of the plant, it is termed an herbaceous perennial. 
The stem may hold itself erect, either by the formation of wood or 
merely by its soft tissues being distended with watery contents ; or 
it may lie prostrate on the ground, in which case its growing apex 
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