176 METABOLISM 



composition, the fats and the carbohydrates (we will deal with the organic 

 acids in succeeding lectures). It requires no depth of chemical knowledge to know 

 that the wealth of chemical compounds in the plant is not thereby exhausted. 

 One need only refer to the odours which are peculiar to so many plants to 

 recognize at once a large series of bodies of wide distribution, such as ethereal 

 oils, resins, &c. Further, we must not forget the colouring matters, which 

 make their appearance in such variety, not only in the flower region, but in the 

 vegetative organs as well, taking the place of chlorophyll. Finally, we are 

 acquainted with bodies to which many plants owe their poisonous or curative 

 powers, the glucosides and alkaloids. Since such substances appear to occur 

 again and again under the same conditions in the same plant, they, as well as 

 sugar, proteid, &c., must be products of metabolism, and the same questions 

 must be asked about them, viz. how are they formed ? What becomes of them ? 

 What significance have they in the plant economy ? Although we have not 

 entered into a discussion of these questions in our consideration of the metabolism 

 of the green plant it is not because they are without interest, but because the 

 researches which have been hitherto carried out on them have led to no, or 

 only to indifferently, conclusive results. We know that many of these bodies 

 do not undergo any further transformation in the plant, we may consider 

 them as final products of no value, as excreta in short. [Many glucosides, 

 hitherto regarded as waste products, act as reserves according to Weevers 

 (1904.)] Such a purely chemical conception is, doubtless, one-sided. The cell- 

 wall in the majority of cases is not further altered in the course of metabolism, 

 but no one would consider it as an excretion, since it is of the very highest 

 importance in the life of the organism. Many such examples might be brought 

 forward ; and it follows that the so-called biological significance of materials 

 demands notice, and this is true especially for such substances as scents, 

 colouring matters, alkaloids, and glucosides, and their significance has been 

 often looked for and found with greater or less success. To enter into that 

 aspect of our problem would take us too far and so we must content ourselves 

 with this brief summary. We may at least draw attention to some of the more 

 important works on the chemistry, physiology and biology of these metabolic 

 end-products [Czapek, Biochemie], such as ethereal oils, resins, &c. : — 

 TscHiRCH, 1900 : Die Harze und die Harzbehalter, Berlin ; H. Muller, 

 1873 : Die Befruchtung der Blumen, Leipzig ; Detto, 1903 : Flora, 92, 147. 

 Colouring matters : — Roscoe : Ausf. Lehrbuch d. Chemie, vol. 8, 1901 ; H. 

 Muller, 1873 : Die Befruchtung der Blumen, Leipzig ; Stahl, 1896 : Bunte 

 Laubblatter (Annales Buitenzorg, 13, 137) ; Alkaloids and glucosides : — RoscoE : 

 Ausf. Lehrbuch d. Chemie, vol. 8, 1901 ; Van Rijn, 1900 : Die Glykoside, 

 Berlin ; Pictet, 1900 : Die Pflanzenalkaloide, Berlin ; Stahl, 1888 : Pflanzen 

 und Schnecken (Jen. Ztschr. f. Naturw. 22). 



Bibliography to Lecture XIV. 



Balicka-Iwanowska. 1903. Bull. Acad. Cracovie. 



Czapek. 1897. Sitzungsber. Wien. Akad. Math.-nat. CI. 106, I, 117. 



Fischer, Alfr. 1890. Jahrb. f. wiss. Bot. 22, y;^. 



Fruwirth and ZiELSTORFF. 1901. Versuchsstationen, 55, 9. 



Gaucher. 1900. Annal. So. nat. vii, 12, 241. 



Haberlandt. 1883. Sitzungsber. Wien. Akad. Math.-nat. CI, I, 87, i. 



[Haberlandt. 1904. Physiol. Pflanzenanatomie, 3rd ed. Leipzig.] 



Hartig, Th. 1858. Bot. Ztg. 16, 332. 



[Kniep. 1905. Flora, 94, 129.] 



KoRNicKE. 1 90 1. Sitzungsber. Niederrhein. Gesell. 



KosuTANY. 1897. Versuchsstationen, 48, 13. 



MiEHE. 1901. Flora, 88, 105. 



Muller-Thurgau. 1882. Landw. Jahrb. 11, 751. 



[Nathansohn. 1904. Jahrb. f. wiss. Bot. 39, 607.] 



