26 THE FLOWERING PLANT. 
adhesive dises at the ends of the tendril branches. Leaf-tendrils 
will be spoken of in another place, as also will leaf-climbers 
generally, in which the leaves are used for ascending, with or 
without the development of tendrils. Root-climbers make another 
class, and ivy is the best-known example. Lastly, we have hook- 
climbers, as in the cleaver or goose-grass (Galiwm), where innumer- 
able minute hooks grow out from the superficial part of the stem. 
We now come to subterranean or underground stems. ‘These 
come under four categories—corm, bulb, rhizome, and tuber. A 
corm, like that of the crocus, is a solid, rounded, main axis, full 
of reserve materials. Adventitious roots grow from its lower 
surface, and there are a few scaly leaf-bases upon its exterior, in 
the axils of which young corms may be formed as fleshy buds. 
From the upper surface a flowering shoot proceeds, and several 
internodes at the base of this thicken into the main corm of the 
following year, to which a shrivelled remnant of the main corm 
of the previous year may adhere. In the sowbread (Cyclamen) a 
vertically-flattened corm is present. A bulb resembles a corm 
in being a condensed stem, but differs from it by being mainly 
composed of thickened leaves or bases of leaves, surrounding a 
flattened disc-like stem. A rhizome differs from the two pre- 
ceding in direction and form. Instead of being vertical, it is 
oblique or horizontal, while its internodes are often of consider- 
able length, and its shape more or less. cylindrical. It may 
either be thin, as in mint and sedges, or else thick, as in the iris 
and Solomon’s seal. Zubers resemble corms in structure, but 
differ from them in being thickened branches. The Jerusalem 
artichoke and potato are good examples, and in both these cases 
several internodes are dilated, while the leaves borne upon the 
nodes are scale-like, and axillary buds, popularly known as 
‘“‘eyes,” are developed in their axils. Some,tubers, however, con- 
sist of only one internode thickened. In a potato plant grown 
from an eye only adventitious roots are present, but in examples 
raised from seed there is a well-developed branching main root. 
By heaping earth around a tuberous plant, branches with tubers 
upon them can be formed higher up than would otherwise be the 
case. Bulbs, thickened rhizomes, and tubers all (like corms) 
serve as stores of nutriment, chiefly starch. Other reserve 
materials may also be present. For example, in potatoes many 
of the cells immediately within the rind contain minute cubes or 
crystalloids composed of proteid matter. The term crystalloid is 
used because, although the form is crystalline, yet the bodies in 
question are not hard, but possess the power of absorbing water 
with consequent swelling up. It is obvious from the above that 
the ordinary method of peeling potatoes, instead of cooking them 
