256 J. H. Priestley and L. M. Woffenden 
portions of tubers bearing buds most readily grow together by in¬ 
tumescence-like outgrowths. The production of this excretion 
probably explains Olufsen’s observation that the larger the wound 
the moister it must be kept to enable it to heal, also the prompter 
rate of healing shown by new potatoes when compared with last 
year’s tubers of the same variety. The use of such an excretion in 
the necessary cell proliferation may also explain Kabus’ observa¬ 
tion, cited above, that the two halves of the “Magnum bonum” 
cylinder only reunited if a tracheid appeared at one cut surface. 
Haberlandt ( 7 , 8, 9 ) has also emphasised the dependence of cork 
formation upon a supply of substances from the vascular strand 
though he traces these substances to the phloem elements. 
The case for the necessity of such an accumulation of sap to 
initiate the meristem activity is much strengthened if we extend our 
observations from the case of the potato tuber to the more general 
phenomena of wound healing. Here again the same two processes 
may be traced, first the closure of the wounded surface and secondly 
the appearance of the meristem. As the available data are less 
complete we will quote chiefly from our own experiments. The first 
closure of the wound again appears to be due to a deposit of suberin 
or some allied substance. Kabus found that this substance did not 
stain with Sudan III: in our experiments the brown deposit resisted 
concentrated sulphuric acid, went brown with iodine reagents, and 
frequently stained with Sudan III. We probably have to do, how¬ 
ever, with a mixture of substances, in part produced by chemical 
decomposition in the dying cells at the cut surfaces, in part 
deposits from the excreted sap which evaporates at the exposed 
surface. 
The following experiments explain themselves, in the light of the 
previous discussion. On March 21st, the epidermis was scraped off 
a long stretch of the stem of a begonia growing in a greenhouse. 
The exposed surface was partly covered with melted paraffin wax. 
On April 25th the two surfaces showed marked differences, the 
waxed surface being very much less brown. On staining sections 
with Sudan III the outermost layer of collenchyma only was slightly 
suberised under the wax, and the five to six layers of cells below 
this, formed by the phellogen, were quite free from suberin. At the 
unwaxed surface more layers of cells bore a deposit of suberin, 
fewer cells had been formed by the phellogen but the outer two or 
three layers of periderm were strongly suberised. The slight suberisa- 
tion under the wax may probably be accounted for by the gradual 
