26 THE FLOWERING PLANT. 



adhesive discs 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 (Galium), 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 

 interiiodes 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. Tubers 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 



