94 Report of Schimmel 8j Co. 1921. 





another, and 2. the poecilophagi, which attack many plants of the most diversified 

 families. To the second group belong among others the insects of the soil, such as 

 mole crickets, the larvas of cockchafers and wire-worms which eat almost anything that 

 their jaws are able to deal with. 



In agreement with other authors 1 ) Zacher accentuates that much injury to plants 

 may be evaded by providing in the cultivation for the best possible conditions. This 

 is all the more important, because just the cultivated plants which are crowded in a ' 

 narrow space, offer good opportunities for the propagation of the insects and are hence 

 more exposed to their attacks than the wild-growing plants. 



Of the examples quoted by the author Valeriana and Mentha are of special interest 

 for us. Valerian is relatively disliked by insects. Its leaves are eaten by four caterpillars 

 of butterflies, viz. the caterpillar of the Melithcea dictynna, S., which is provided with 

 spikes, the caterpillar of a moth (Caradrina quadripunctata, F.), a "looping" caterpillar 

 (Tephroclystia valerianata, Hb.) and the caterpillar of a small butterfly (Depressaria pul- 

 cherimella, Stt). A gall mite {Eriophyes macrotuberculatus, Nal.) causes the flowers to 

 turn green, whilst the development of the axis of the inflorescence is prevented by the 

 larvas of the gall-gnat (Contarinia valerians, Rubs.); the flowers are then crowded and 

 remain barren. In the stalk of the mint lives the larva of a beetle with a sorex trunk 

 (Apion vicinum, Kby.) and causes an oval or coniform swelling, more or less red in colour, 

 above one of the upper knots. The leaves are eaten by two leaf flees (Longitarsus 

 Waterhousei, Kutsch. and lycopi, Foudr.) and also very largely by the beautiful big blue 

 beetles of the species Chrysomela ccerulans, Scriba, and their variety, Menthastri. Suffr., 

 which are often of a golden lustre. On Mentha we further find the prickly mud-covered 

 larvae of two bugs (Cassida viridis, L. and Murrcea, L.). In addition quite a dozen of 

 butterfly caterpillars, the enumeration of which would lead us too far, feed on the mint. In 

 the swollen buds which then remain closed is found the ochre-yellow larva of a gall-gnat 

 (Asphondilia menthce, Pierre). Two gall-gnat species produce galls in sprouts and leaves. 



Phytophysiological Notes. 



According to all experience the essential oils are by-products and final products 

 of the plant assimilation. As regards their mode of formation it is only known that 

 they are formed like the balsams and resins, partly in the interior of the protoplast, 

 subsequently to coalesce to homogeneous masses of oil and balsam, or to remain in 

 a state emulsion as in milk saps. The plants, however, also secrete substances which 

 outside the protoplast are either converted into essential oils or balsams, or which take 

 their origin from a metamorphosis of the cell membrane 2 ). Frequently the essential oil 

 of the living cell is changed by exposure to the air, as, for instance, in the camphor 

 tree where it is converted into camphor by post-mortal absorption of oxygen. 



As regards the ecological importance of essential oils, that is, their importance in the 

 external life of the plant, we take a few statements from an article by N. Patschowsky 3 ). 

 Whilst the oils of agreeable scent, present in the petals, allure insects chiefly for as- 

 phyxiation, the essential oils present in the vegetation-organs of the plant are credited 

 with various other tasks. Some authors presume that the essential oils, which are 

 formed in the epidermal glands of the plants, are to protect them against overheating 

 and excessive transpiration. More probable than this somewhat dubious hypothesis is the 

 view that the odorous substances are able to keep deleterious organisms at a distance. 



x ) Report 19-20, 107. — 2 ) Pfeffer, Pflanzenphysiologle. 2 nd ed., vol. I, p. 501. — 3 ) Naturw. Wochenschr.. 

 1920,497; from Naturw. Umschaa d. Chem. Ztg. 9 (1920), 134. 



