216 STUDIES IN PLANT REGENERATION 
roots, where, after the removal of a piece from the tip of between 
I mm. and 2 mm.,a single root may form from the cut instead of 
more, as is common. No case has been found by the writer in 
which a single organ is recorded as coming from the stem, when 
all of the root had been cut off. Here the sympodial character of 
the regenerated organ becomes obscured and the seedling exter- 
nally resembles the uninjured one in all essentials. 
Experiment ҙ2.-- Тһе stems of each of the three-year-old 
plants of this pine were cut into four pieces and planted. АП of 
these produced slight calluses, but in the two lower sets no roots 
formed, even when the callus was again wounded. One of the 
apical pieces, however, formed a root directly from the stem 
above the callus — a phenomenon that has been often observed in 
other instances ; and іп one of the second set, as in the seedling, 
a single root appeared from the middle of the callus which grew 
so as to occupy the entire cut surface, again restoring the plantlet 
to its original condition (Fig. 9, 6). Thus there seems to be а 
tendency in this pine to form only one root from the callus produced 
as a result of injury. Not many instances of this restoration in 
adult tissue are known. 
The great majority of plants with aerial stems (the beech is 
the best known exception) — are capable of being propagated from 
stem-cuttings. It is, therefore, instructive to reflect that this power, 
is, in at least a large percentage of cases, due entirely to the pres- 
ence of shoot-buds on the part before the cutting is made. This 
is not universally true. The cut-stems of poplars, elms, and 
other trees are known to develop shoots from a callus on their 
apical cutends ; and Vochting obtained shoots from the internodes 
of Begonia discolor. But in most cases, when such buds аге 
removed, the stems seem to be incapable of replacing them, and 
the cuttings fail to establish themselves as plants. Тһе behavior 
of such parts serves to emphasize the principle that while unfavor- 
able external conditions may prevent a normal regeneration or 
cause a change in its position, even the most auspicious culture 
conditions fail to induce such a formation when the internal A 
is lacking. 
ЖЕ. Е, 5 
