STUDIES IN PLANT REGENERATION 201 
tion to developing the rudiments already formed. The power of 
forming the shoots lies in the cambium at the cut, and in the callus 
formed as a result of the injury, when no cambium layer is pres- 
ent. It will also be noticed that the tendency to produce shoots 
at the apical end of a horseradish root- 
cutting is at least as strongly marked as 
that Operative at the basal end. 
In the sweet potato (/pomea Bata- 
tas) and dahlia (2. variabilis) we have 
examples of thickened secondary roots 
which develop shoot buds between 
growing seasons, but care was taken 
that none should be present in the parts HIT 
used in the experiments. The cuts жо, 2, Central tissues of 
made were similar to those described іп root of Roripa 22 from 
the horseradish. which the rind an cambium 
Experiment з. —Transverse sections е яз dn rae 
of sweet potatoes between 2 mm. and 
3 mm, in height were placed underneath the level of the sand. 
Although a large number of these pieces grew moldy and 
decayed at once, a small proportion continued healthy and in 22 
days produced roots. Many of these roots were true regenera- 
tions, inasmuch as they did not arise from the cambium and grow 
outward, after the manner of normal secondary roots, but ap- 
peared in the middle of both lower and upper cut surface. Micro- 
Scopical examination showed that a callus of about four layers of 
cells had been formed on each surface whence the Foo took 
their origin. Тһе parts decayed without shoot-production. 
Experiment 4. — The rind in which the buds appear was next 
removed from six of the tubers, and the pared parts were planted. 
Again roots were produced in numbers, but no shoots were formed 
іп the four months before the cuttings decay ed. а TE: 
Experiment 5.-- The converse of this experiment was à is 
tried. Thin rind pieces, without visible buds and as far as pes 
ble freed from underlying tissues, were covered with sand. 22 
also rooted within two weeks, but during the two months in whic 
the parts remained intact, no shoots appeared. о ras 
of the parts of sweet potato in which shoot-buds were lacking 
ever regenerated such buds in these experiments. 
