DIV. II 



PHYSIOLOGY 259 



insectivorous habit would have to be sought in the provision of more 

 nutrient salts than are afforded by the soil. 



The insectivorous plants strike the ordinary observer as deviating 

 from ordinary plants in the direction of the animal kingdom. Like 

 animals they utilise solid food which has to be rendered fluid by 

 enzymes before it is absorbed into the cells. The similarity between 

 animals and these plants appears to be increased by a comparison of 

 the stomach and the pitchers, etc., of some insectivorous plants. It 

 should be recognised, however, that some Fungi and Bacteria stand 

 physiologically closer to animals. They can obtain all their food by 

 the digestion of solid organic material, while the insectivorous plants 

 are autotrophic, at least as regards their supply of carbon. 



In relation t<^ insectivorous plants certain phanerogamic parasites 

 may be considered which were omitted above (p. 254), since they 

 possess green leaves and are evidently autotrophic as regards their 

 supply of carbon. In spite of this, however, the plants only develop 

 normally, when their root-system is in connection with the foots of 

 other plants by means of disc-shaped haustqria. They may even (as 

 is also the case with Cuscuta) enter into this relation with other 

 individuals of the same species. Thesium, belonging to the Santalaceae, 

 and the following genera of the Rhinanthaceae, Bhinanthus, Euphrasia 

 Pedicularis, Bartsia, and Tozzia, may be mentioned as examples of 

 plants showing these peculiar conditions. In Tozzia the parasitism is 

 well marked in the earliest developmental stages. The Mistletoe 

 (Viscum album), although strictly parasitic, possesses, like many of the 

 allied foreign genera of the Loranthaceae, fairly large leaves well 

 supplied with chlorophyll, and quite able to provide all the carbo- 

 hydrates required. By its reduced root-system it obtains, however, 

 from the host plant (as has also been shown to be probable in the 

 case of the Rhinanthaceae ( 36 )) its supply of water and dissolved salts. 



In contrast to these plants, which are either demonstrably or probably 

 supplied with organically-combined nitrogen, there are certain micro- 

 organisms which are strikingly autotrophic as regards nitrogen, while 

 they are heterotrophic as regards their carbon assimilation. These 

 organisms are able to utilise the nitrogen of the atmosphere. Their 

 existence was first established at the end of last century by the work 

 especially of WIXOGRADSKI, HELLRIEGEL, and WILFARTH ( 3T ). 



In the first place there are certain Bacteria, such as Clostridium 

 Pasteurianum and related forms and Azotobader chroococcum, which live 

 independently in cultivated soil and in water under very various 

 external conditions. They fix free nitrogen and thus possess a 

 very important power both for their own success and for that 

 of many other organisms ; this property is of the greatest importance 

 in agriculture. An increasing number of the lower Fungi have been 

 shown by recent researches to have the same power though in less 

 degree. In addition to these free-living forms there are micro-organisms 



