186 Principles of Plant Culture. 
plants, as the potato, grape etc., normally develop growing 
points of roots at their nodes (116). Plants that normally 
develop buds upon their roots or growing points of roots at their 
nodes are readily propagated by cuttings. But propagation 
by cuttings is not limited to such plants (362). 
360. The Essential Characteristics of a Cutting 
are a—a certain amount of healthy tissue; 6 —a certain 
amount of assimilated food, or of tissue capable of assimi- 
lation, i. e., chlorophyll-bearing (green) tissue; ¢e—in most 
species, a growing point (67), either of the stem or root, or 
of both. 
361. The Parts of plants to be Used for Cuttings, 
therefore, are preferably the younger, matured growths, 
since the tissues of these are most vigorous; or else a part 
that possesses a certain amount of healthy and vigorous 
leaf tissue. The cutting should always contain one or more 
buds when practicable (128). 
362. Conditions that Favor the Growth of Cuttings. 
a—A soil warmer than the air above it (‘bottom heat’’) is 
important in growing plants from cuttings. Warmth stim- 
ulates plant growth, and when applied to one part of a plant, 
it stimulates growth in that part. If the soil about a planted 
cutting is warmed to a temperature considerably higher 
than that of the air above, the growth of roots is stimulated. 
Indeed bottom heat often excites growth in cuttings that 
will not grow without it. 
b— A comparatively low air temperature is important in 
growing plants from cuttings of the stem (377) because it is 
essential that the stem growth be held in check until roots 
are formed. A soil temperature of about 65° F., with an air 
temperature about fifteen degrees lower, is suited to the great 
a 
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