McCALLUM—REGENERATION IN PLANTS 243 
1905] 
basal primordia in the air below promptly developed. When the 
hydrogen was removed, the apex continued growing. Placing the 
roots in plaster, which inhibited any further growth on their part, 
also resulted in the development of roots along the stem. In these 
cases there was no wounding anywhere. It appears that while regen- 
eration follows the removal of certain parts, neither this removal nor 
the wound incident to it are necessary, since the regeneration occurs 
equally well when the part is left uninjured and certain of its activities 
suppressed. The wound, therefore, is not in itself any part of the 
stimulus. 7 
CORRELATION. 
By correlation is meant the influence which one organ or part 
may exert over another. That the removal of certain parts leads to 
changes within the plant that may modify markedly the growth or 
function of other structures is a matter of common observation. 
Examples of this interdependence among the different members of 
the plant body are abundant. Jost (8) has shown that in Phaseolus 
the mere presence of the leaf is a necessary condition to the develop- 
ment of the bundles of the leaf trace. P1sCHINGER (16) determined 
that if the large cotyledon of Streptocarpus be removed the small 
functionless one will develop into a large one. According to GOEBEL 
(6, p. 809) the early removal of foliage leaves induces the bud scales 
to develop into the foliar structures. If the upper end of a Taraxacum 
Toot be cut away, removing all the buds, new buds soon arise from 
the cortex below; this is true of many roots. IrmiscH and others 
(10) have shown in many species that if seedlings be cut off below 
the first node, new buds arise out of the tissue of the hypocotyl. The 
Temoval of the growing tip on many shoots is followed by the 
development of the dormant axillary buds. As is commonly observed 
ln cultivation, if the lateral roots be destroyed, their place is taken 
ta sa roots, which otherwise would not have developed. GOEBEL 
eR 5) showed that in Begonia and Bryophyllum, and this 1s 
y true for many other plants, the removal of all the buds on 
“0 will result in the development of buds on the leaves. 
sie — by which such an influence is exerted by one part 
a er is the main problem to be solved in regeneration. 
attempts to explain it in one of two ways: either (1) the one 
