243 



I repudiate any suggestion that the taxonornic evidence afforded by the 

 morphology of plants can be intelligently studied except in connection with such 

 physiological evidence as may be available. 



At the same time, the classifactory characters must be mainly morphological. 



" But in his clear definition of the principles which must guide the worker who is seeking a true 

 natural system, De Candolle did work of far greater value. He pointed out that characters which are of 

 the utmost importance to the life-functions of the plant are useless from a systematic point of view. In a 

 word, it is to morphology, and not to physiology, that wo must look for aid in establishing relationships."* 



Oil an accessory or adaptive character. 



The essential oils arc accessory substances, and, may I repeat it, variable like 

 everything else connected with Eucalyptus. 



1. The chemical qualities, odours, and tissues of plants are often modified by a change which 

 seems to us slight. The Hemlock is said not to yield conicine in Scotland. The root of the Aconitum 

 napcllus becomes innocuous in frigid climates. The medicinal properties of the Digitalis are easily 

 affected by culture. The Rhubarb flourishes in England, but does not produce the medicinal substance 

 which makes the plant so valuable in Chinese Tartary. As the Pistacia lentiscus grows abundantly in the 

 south of France, the climate must suit it, but it yields no mastic. The Laurus sassafras in Europe loses 

 the odour proper to it in North America. Many similar facts could be given, and they are remarkable 

 because it might have been thought that definite chemical compounds would have been little liable to 

 change either in quality or quantity. f 



2. Just as the presence and quantity of opium, hasheesh, aconitine, &c, secreted by plants, vary 

 greatly with the climate, so it is reasonable, in the absence of strict investigations, to assume that these 

 oils are in an excess through the intense heat, and other conditions of the climate of deserts.} 



3. Interesting as is this correlation of morphology and constituents in the Eucalyptus species, it 

 may be pointed out that a knowledge of the constituents of a plant is never likely to play such an 

 important part in systematic botany as the authors appear to believe, since there arc already known 

 numerous instances of plants which, grown under different climatic conditions, show no morphological 

 change, yet exhibit remarkable variation in constituents, and, on the other hand, plants which are not at 

 all closely related frequently contain the same colouring matters, alkaloids, etc., so that the necessary 

 specific constancy of constituents, which alone would make such criteria useful, is wanting. The authors 

 lay stress on observations made by them as to the absence of marked variation in the composition of oils 

 yielded by the same Eucalyptus species grown in different districts of Australia ; but the evidence of 

 constancy in this respect would be greatly strengthened if it could be shown to hold for the same species 

 outside Australia. For an investigation of its kind ample material now exists in foreign plantations.§ 



The cases of the Peppermint and Lavender, both plants yielding essential oils, 

 are notorious. Science has not yet established a connection between morphological 

 characters and oil-yields in these cases. 



It is only necessary to consult any good work on essential oils, say Die 

 cetherischen Oele, E. Gildemeister and Fr. Hoffmann (Julius Springer, Berlin), of 

 which the authorised translation is The Volatile Oils, by Edward Kremers (Pharm. 

 Review Co., Milwaukee, U.S.A.), and especially Schimrael's Semi-annual Reports 



• Bendle's Flonx ring Plants, vol. i, p. 12. Page 16 of this work may also be referred to. 

 t Animals and Plants under Domestication. Darwin, vol. ii, p. 274. 

 J Origin of Plant-structures. Hcnslow, p. 82. 



§ Review on "A Research on the Eucalypts, especially in regard to their Essential Oils" (Baker and Smith), by 

 Dr. T. A. Henry, in "Nature," vol. 07, April 2nd, 1903, p. 525. 



