126 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



the liberation of indigo in the solid form. So easily is the effect produced 

 that it may well be that a lowering of the cell's vitality is sufficient to 

 bring about the decomposition of the glucoside, and this supposition is 

 supported by other evidence. The precipitation of indigo in the cells 

 furnishes a very convenient index of the progress of local death in any 

 part ; it is evident even in some cells which are still green and not yet 

 plasmolysed, whereas in others the decomposition of the indican takes 

 place after plasmolysis. This is not the time to discuss the use and 

 destiny of such a glucoside as indican. If it is made use of by the 

 plant in metabolism, its decomposition must be of a different character 

 from that noted here, for indigo is not found in the vitally active cell. 

 It is not unreasonable to suppose, therefore, that the decomposition of 

 indican with the production of indigo, however brought about, may be a 

 cause as well as an effect of the death of the cell. Indigo is certainly 

 never found in cells which continue to live. 



The majority of the Calanthe plants which have been under my 

 observation, in consequence, as I believe, of previous wrong methods of 

 cultivation, develop their leaves irregularly. The outer protecting leaves 

 of the bud develop and open out so slowly and imperfectly that the 

 inner leaves are crowded and cannot emerge properly. This causes much 

 injury to them, so that tips and edges are frequently damaged before they 

 see the light. Young hairs are also torn away in consequence of im- 

 perfect plaiting, and wherever a hair is torn a dead spot appears and 

 extends. 



But, beyond this mechanical injury, the young leaves before emergence 

 show a multitude of pale spots, more transparent than the surrounding 

 tissue, and manifesting a deficiency of chlorophyll. Although the cells of 

 these spots grow for a time, they grow more slowly than the healthy cells 

 around them, and in consequence strains are produced which destroy the 

 parallelism of the fibro-vascular bundles' on each side of them. Yet the 

 transverse branches which pass through the unhealthy tissue and connect 

 the parallel bundles appear to grow to their full length, and in order to 

 be accommodated in the narrowed space they pursue a tortuous course 

 with many angles, approaching in places near the surface of the leaf. At 

 an early stage the unhealthy cells become plasmolysed, their indican — 

 which is not present in so large a quantity in them as in the healthy 

 cells — is decomposed, the cells die and the tissue is frequently ruptured. 

 As the leaf grows other pale spots appear, and the whole of the spots, 

 extending into each other, form large or long black dead blotches. By 

 steeping the leaf in alcohol, or by boiling it in alcohol for a few minutes, 

 the dead cells can be seen to be full of indigo. 



In the progressive death of the leaf from the tip or edge, or from a 

 dead spot, the first visible difference beyond the obvious dead margin is the 

 deposition of indigo -blue in the cells. This is first seen in elongated 

 cells about the fibro-vascular bundles, and in the guard-cells of the 

 stomata on the still green side of the margin. Plasmolysis of the cells 

 and the disappearance of air from the intercellular spaces extend also 

 some little distance into the still green tissue. 



The imperfect development of the leaf-bud, and the appearance of 

 diseased places in the very young leaf, are certainly determined by an 



