REGENERATION OF THE VEGETATIVE POINT 43 



I. REGENERATION OF THE VEGETATIVE POINT. 



Regeneration obviously takes place most easily in embryonal tissue, 

 and it is of interest to note that those parts of the vegetative point are 

 able to share in it which by their position in the higher plants we know 

 to be already on the way to produce definite systems of tissues. After 

 Ciesielski had first observed that a new root-apex appeared after some 

 days upon roots whose tips had been cut off, Prantl l made a careful 

 investigation of the process. He found that a complete restoration of 

 the root-apex, in which all the layers of tissue have a share, takes place 

 if the cut is carried through that point where the curved arrangement 

 of the cell-rows of the vegetative point of the root passes over into a 

 straight one. A slight growth takes place by which a ' callus ' of 

 embryonal tissue is formed, and in this a new vegetative point for the root 

 subsequently appears in the position of the old one, so that the new root- 

 apex has quite a normal appearance. Occasionally instead of one apex two 

 may be developed, and it would be of interest to know, could it be 

 determined, under what conditions this is brought about. If the cut is 

 carried through at a further distance from the root-apex there is no 

 restoration of the lost point, but primordia of one or more rootlets 

 proceed from a growth of tissue which develops from the primordia of the 

 procambial bundles. If the cut be still further from the point there is 

 generally no regeneration at all, and this I believe is connected with 

 the fact that in such positions the primordia of the lateral roots are 

 already existent and one of them takes on the function of continuing the 

 chief root, and therefore restoration of the chief root is suppressed. 

 When the new vegetative point continues the root in the place of the old 

 one, it must obviously do this under the influence of such parts of the 

 old root as remain behind. If a root be split longitudinally the halves 

 regenerate themselves, provided that they retain a portion of the apical 

 region 2 . 



The prothalli of ferns behave in quite the same manner. If we split 

 longitudinally the heart-shaped prothallus of one of the Polypodiaceae 

 and remove a lobe, a regeneration of the vegetative point takes place ; 

 a new lobe is then formed out of the restored vegetative point and the 

 prothallus acquires the original form again in its anterior portion, whilst 

 no restoration of the older parts that were removed takes place. This 

 incapacity to repair mutilations in old parts, which distinguishes plants 



1 Prantl, Untersuchungen iiber die Regeneration des Vegetationspunktes an Angiospermenwurzeln, 

 in Arbeiten d. botan. Instituts in Wiirzburg, Bd. i. 



2 For anatomical relationships, see Lopriore, Uber die Regeneration gespaltener Wurzeln, in Nova 

 Acta Acad. Leop.-Carol. Ixvi. No. 5. 



