DISEASE OF THE LEAVES OF CALANTHES. 



125 



of the young leaf, but they are not persistent. The bundle system is 

 fairly well developed, although the transverse branches between the 

 parallel bundles are very rudimentary, consisting mainly of a single row 

 of imperfectly formed tracheides. 



Regarding its structure, therefore, it is a leaf which is calculated to 

 perform its vital functions most efficiently in a well-shaded position and a 

 moist atmosphere. 



The deciduous section lose their leaves shortly after the completion of 

 growth of the pseudo-bulbs. This, and the presence of a large pseudo- 

 bulb and a well-developed root-system, show that the plant should be 

 classed as a tropophyte — one of those which pass through a dry (or cold) 

 season of no growth, and a wet (or warm) season of exuberant growth. 



It would appear, therefore, from the consideration of the plant's 

 structure, that the most favourable conditions of cultivation would be an 

 easily rooting medium such as is now generally used for Orchids ; plenty 

 of water at the roots when root-action is vigorous ; a well-shaded position 

 at all times ; and a moist atmosphere during the whole period of leaf- 

 growth and leaf -action. Orchid manuals recommend that manure should 

 be mixed with the potting soil, and that liquid manure should be given 

 when the bulbs are swelling. I regard manure for these plants as not 

 only not necessary, but distinctly harmful. It is also recommended that 

 the plants should be close to the glass on the lightest side of the stove, 

 and the general practice is to give Calanthes too much light. It is well 

 known that the intensity of the chemically active solar rays in this 

 country during a bright summer is nearly equal to that in the tropics. But 

 Calanthes cannot endure such insolation without injury. Ewart showed* 

 that the effects of excessive insolation are the inhibition of carbon assimi- 

 lation and, in many cases, the complete destruction of the chlorophyll. 



It is certain that very slight injury to the leaves is invariably followed 

 by the^ieath of the injured parts, and that death is not confined to the 

 portions injured. For example, a slight puncture with a needle causes in 

 a few days the destruction of a portion of the leaf several millimetres in 

 diameter. An injury to the leaf -point or edge is followed by a progressive 

 death of the leaf, which continues as long as the leaf remains on the 

 plant. This increasing effect of slight injury is not confined to the leaves, 

 but is evident also in the roots, flower-stems, and bracts, and in the floral 

 segments. In this respect it is interesting to note that the various 

 Phaius species and hybrids behave in a similar manner. 



Schunck, in 1901, noticed that the leaves of Calanthe veratrifolia and 

 Phaius grandifolius contained indican, a glucoside, which under the 

 influence of oxygen — always present in the intercellular spaces of the 

 plant — decomposes spontaneously, with the production of insoluble indigo, 

 as soon as the vitality of the cell is destroyed. I find that indican is 

 present in all the parts, including the flowers, of the Calanthes in question, 

 as well as in Phaius tuberculosus, P. Warvuri, varieties of P. grandi- 

 folius and their hybrids. So unstable is the glucoside that a slight rub 

 with the finger along the labellum of a Phaius flower causes in a very 

 short time the appearance of a dark-coloured blotch in consequence of 



* Annals of Botany, 1897, p. 439. 



