HISTORY OF THE PLANT KINGDOM 307 
usually three sets of vegetative organs, — roots, stems, and 
leaves. Not infrequently, as in the ivy (Fig. 13), some of 
the roots perform the work of absorbing soil water, while 
others serve to aid the plant in climbing. Some plants 
produce both parasitic roots and ordinary roots for absorp- 
tion of water from the soil. Stems may in the same plant 
function as subterranean storehouses of reserve material 
and as aérial supports for leaves: (Fig. 33). In Myrsi- 
phyllum (Fig. 37), butcher’s broom, and a good many other 
plants, parts of the stem serve to support in an advan- 
tageous position other flattened portions which are special- 
ized for photosynthesis instead of leaves. Ordinary stems 
may, as in the grapevine and the woodbine, produce special 
branches (tendrils) which serve as aids in climbing, and 
the hawthorn, the crab apple, and the honey locust develop 
dwarf branches in the form of thorns. It is especially 
worth while to call attention to the fact that in seed-plants 
the variety of forms and functions of leaves on the same 
plant has reached a climax. For instance, in such a plant 
as the lily, the lily-of-the-valley, or the star-of-Bethlehem, 
we find scale leaves, foliage leaves, bracts, perianth leaves 
(often of two kinds), and sporophylls (stamens and pistils). 
It is difficult or impossible for the mind to grasp the 
entire set of codperative activities which go on at every 
moment during the growing season in any large and highly 
organized plant. Suppose, for example, that all the living 
parts of an immense pine tree could be seen in action just 
before the beginning of its period of flowering. From the 
tips of the rootlets to the tips of the leaves, a hundred 
and fifty feet above, many millions of cells are performing 
the operations of absorbing soil water, conducting it up- 
ward, manufacturing plant food by complicated chemical 
