86 PHYSIOLOGY OF NUTRITION. 



sickness, since particularly the youngest, and later also the older 

 leaves, become spotted with brown. The leaves obtained have 

 about the same size, and also contain the same quantity of chloro- 

 phyll as those formed tinder normal conditions. They can 

 assimilate, like these latter, but still ultimately die off. The leaves 

 of plants grown without lime differ from normal leaves in being 

 very rich in starch. The brown stains which after a certain time 

 appear on them, are, as the investigations of Schimper and Loew 

 seem to show conclusively, due to action on the tissues of injurious 

 organic acids, especially Oxalic acid. Organic acids are of course 

 abundantly formed in plant metabolism. They must be neutral- 

 ised, and the function of the lime is especially to effect this. If 

 the neutralisation of the acids is not affected, some processes in 

 the cells are arrested, and finally the cells completely die off. 

 Lime is also of importance in the nutrition of plants, inasmuch 

 as inorganic acids (Nitric and Sulphuric) are introduced into the 

 plant chiefly in combination with lime. 



Potash appears to play an important part in the origin and 

 development of plant organs. If we cultivate plants in solutions 

 devoid of potash, their behaviour is quite different to that in absence 

 of lime. At first the Potassium compounds migrating from the 

 older parts still serve to a certain extent to satisfy the require- 

 ments of the new organs. We shall, however, observe that these 

 organs, e.g. the leaves, become smaller and smaller, till finally 

 the plant dies. In the plants raised without potash compounds, 

 the assimilatory activity also gradually ceases (Nobbe, Schimper), 

 but still not till other indications of ill-health are already apparent, 

 especially the limited growth of the new organs. 



1 I have collected the literature on the subject in my Lehrbuch der Pflanzen- 

 pJiysiologie. 



2 See Schimper, Flora, 1890, Heft 3. 



32. The Requirements of Fungi. 



The development of fungi, like that of higher plants, is'Jdependent 

 on the presence of mineral substances capable of absorption. To 

 prove that this is the case we make appropriate culture experi- 

 ments with the yeast fungus (Saccharomyces cerevisias). We 

 prepare a good quantity of a fluid having the following percentage 

 composition : 84 parts of water, 15 parts of the purest sugar 

 candy, and 1 part of Ammonium tartrate. Four flasks are 



