REGENERATION IN PLANTS. I. 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY. 
LXXVI. 
WILLIAM BURNETT MCCALLUM. 
* (WITH FOURTEEN FIGURES) 
INTRODUCTION. 
THE term regeneration has come to be used by most botanical 
writers with a broad and somewhat indefinite application. Its essen- 
tial feature, however, is the replacement of an organ or structure 
that has been removed. This is accomplished in a variety of ways. 
PRANTL (9) first found and later Srmons (11) determined more accu- 
rately that if the tip of a root be cut off not more than 0.75™™ from 
the end there is a complete restoration of the part removed, a new 
tip forming out of the tissues at the cut surface. GOEBEL (3) p- 503) 
has shown that if the young apex of the frond of Polypodium be cut 
in two lengthwise, the remaining embryonic tissue on each piece will 
completely reform the half that has been removed. The same is 
true of the growing point of a fern prothallium, although the older 
parts are not replaced. These phenomena are quite homologous 
with regeneration as it occurs in animals. If we cut off the root tip 
somewhat farther back, however, a new tip is not organized at the 
cut surface, but behind it one or perhaps more new root primordia are 
organized, and these take the place of the main root. Or if we cut 
off transversely a portion of the thallus of Marchantia or Lunularia 
(12), the tissues at the cut surface will not develop, but there will 
arise from apparently mature and differentiated cells back of the cut 
new outgrowths of thallus which again will complete the plant. 
If the shoot with all the buds be severed from the root of Tar- 
axacum, new shoots will arise lower down from the mature tissues 
. = cortex. Many fleshy roots have this capacity, and if cut into 
peng of pieces each will organize new primordia and develop 
j . lf the young stem of Convolvulus, Linaria, and other plants 
aa cut off just below the cotyledons, there will arise on the sur- 
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