186 TRANSACTIONS OF THE [Sess. lxxxvii 



and that under favourable conditions callus forms more readily 

 at the younger parts of the stem. 



Investigation of the internal anatomy of the normal stem, 

 of the same age as that used for propagation, was carried on 

 simultaneously. Camphor, like the other Laurineae, shows 

 quite a normal arrangement of stem tissues, the most noticeable 

 feature being a continuous stereom in the pericycle. This was 

 found to consist of crescent-shaped patches of prosenchymatous 

 elements opposite the phloem, joined by a single layer of 

 U-shaped stone cells (2). It was particularly noticed that 

 although the cell walls gave all the lignin reactions, the cells 

 themselves still retained their protoplasmic contents (fig. 3). 



A series of sections was made from the 1st to the 10th node, 

 in order to trace the process of development of the stereom 

 in the normal stem. No lignification is evident till after the 

 ■Jnd node, and then only in the xylem vessels to a slight 

 extent. About the 3rd node slight lignification appears in 

 the pericycle, in the form of small patches opposite the phloem, 

 gradually increasing and finally linking up, by means of stone 

 cells, between the 6th and 8th nodes. 



In the case of the stem etiolated for fourteen days, no 

 lignification is visible in the pericycle till the 6th node is 

 sectioned, although the vessels of the xylem show lignification 

 after the 3rd node ; and even at the 8th node the crescentic 

 patches are small in size and discontinuous, no stone cells 

 being visible. A detailed examination of the individual 

 cells shows reduction in thickness of cell wall with a corre- 

 sponding increase in protoplasmic content (fig. 4). 



During this partial etiolation, the pericyclic stereom in- 

 variably present at the 6th internode of the normal stem 

 becomes transformed into thin-walled parenchyma. The 

 change is gradual, and at the 8th-10th internodes lignification 

 still persists, but never in a continuous ring. 



>Sections were made of etiolated cuttings in every stage of 

 callus formation. In fig. 5 division is most active in the 

 cambium and inner cortex, where it is seen giving rise to a 

 large pad of callus, wliich will s]«ead to cover the entire 

 wounded surface. Cuttings four days old show a well-formed 

 callus ring with a central discoloured pith. Fig. 6 shows 

 necrotic pith cells with discoloured cell walls extending for 

 a distance of 6-8 nun. from the wound. The pith cells 



