114 PLANT PHYSIOLOGY AND ECOLOGY 



and propagation is largely carried on by the latter. In conse- 

 quence, other kinds of propagules are rare. Buds, bulbils, or 

 bud-like bodies serve for propagation in some ferns. 



137. Propagules of flowering plants. In the spermatophytes, 

 root, stem, leaf, and flower are all capable of producing meris- 

 tematic tissues that may serve as the essential part of a propagule. 

 Probably no plant has the power to develop buds upon all of these 

 organs, and in most cases this ability is restricted to one or two 

 parts. It is a common characteristic of the stem and is often found 

 in roots. It occurs rarely in leaves, at least under natural con- 

 ditions, and is altogether exceptional in flowers. Root buds, 

 i.e.. the use of roots as propagules, are very common in woody 

 plants, both trees and shrubs, such as the aspen, cottonwood, 

 lilac, rose, raspberry, etc., and it occurs also in herbaceous plants 

 e.g., milkweeds, dock, toadflax, and certain composites. The 

 development of plants from root buds often takes place under nor- 

 mal conditions, but it is a regular occurrence when the trunk 

 has been cut down. 



Buds occur on foliage leaves, especially those that are thick 

 or fleshy. They spring usually from the margins, but are also 

 formed upon the surface. Such leaves are regularly used for 

 artificial propagation by florists and gardeners. In nature leaf 

 buds occur regularly on only a few plants, though they have been 

 occasionally observed upon a number of herbs, chiefly among the 

 mustard and lily families. Although some are able to form 

 plantlets upon the leaf while it is still in position, it is evident 

 that propagation by this method would rarely prove successful 

 in nature, except perhaps in wet habitats. The production of buds 

 from floral leaves occurs in but a few genera, and such buds are 

 incapable of propagation without the artificial removal of the 

 carpels. Flowering branches are often replaced by propagative 

 buds in many grasses, in the onion, saxifrage, etc. 



138. Stems as propagules. Bud-bearing stems are variously 

 modified to constitute propagules, of which they are by far the 

 most important source. According to the form which the stem 

 takes, such propagules are termed stolons, offsets or runners, 

 rhizomes, corms, bulbs, and bulbils. The stolon is a descending 

 or trailing leafy branch which forms roots and a shoot where it 

 touches the ground; it is found in many bushes, currants, goose- 

 berries, etc. The runner is a prostrate or decumbent slender leafless 



