HISTORY OF THE PLAXT KINGDOM 307 



usuallj- three sets of vegetative organs, — roots, stems, and 

 leaves. Xot infrequent!}-, 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 aerial 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 ha\^'thorn, 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-vaUey, 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 cooperative activities which go on at every 

 moment during the growing season in any large and highly 

 organized plant. Suppose, for example, that all the liA-ing 

 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 



