100 PHYSIOLOGY OF NUTRITION. 



allowing to dry in the air. We finally put on a drop of oil of tur- 

 pentine and examine under high magnification. 2 



1 See Zopf, in Schenk's Handbuch d. Botanik, Bd. 3, p. 65. 



2 For further information respecting the investigation of Bacteria, see Fliigge 

 Die Micro-organism en, Leipzig, 1886, and Hueppe, Methoden d. Bacterienfor- 

 sclmng, 1886. 



39. Some Parasitic Fungi. 



There are many fungi which are recognised as the causes of dis- 

 eases in plants. They nourish themselves at the expense of the 

 substance of living plants, and therefore must be classed not as 

 Saprophytes but as Parasites. In May and June we frequently 

 observe leaves of Berberis vulgaris which have protuberant 

 cushion-shaped, orange- coloured swellings on their under side. 

 Microscopical examination of delicate transverse sections of a Ber- 

 beris leaf shows that the mesophyll is made up of palisade and 

 spongy parenchyma, and these tissues are also observable in 

 somewhat modified form, it is true in the swollen parts. Here 

 the cell contents (protoplasm and chlorophyll grains) are disorgan- 

 ised, and in the intercellular spaces are present numerous fungal 

 hypha3. These belong to the ^Ecidium generation of Puccinia 

 graminis, which is the f iingus we shall first consider. On treating 

 the sections with potash solution, the relations we have men- 

 tioned stand out with especial clearness. 



On the under side of the cushions we notice peculiar cup-shaped 

 structures, which in their development break through the tissue 

 of the cushion, and finally even through the epidermis of the leaf. 

 Below the cups we see a thick layer formed of hypha3. Each cup 

 itself consists of an investment (peridium) and the numerous spore- 

 producing basidia, which at the base of the cup are associated 

 to form the hymenium. On the upper side of the cushion no 

 ^Bcidium cups are present, but here may be found pear-shaped 

 structures, the spermogonia. 



The spores from the ^Ecidium fruit of Puccinia germinnte from 

 the middle of June on various grasses (wheat, barley, oats, etc.). 

 They attack chiefly the haulms and leaf-sheaths, and cause the 

 familiar disease of grain known as rust. On examination of delicate 

 transverse sections from an oat haulm covered with rust-brown 

 stripes, due to the vegetation of the uredo-layers of Puccinia, we 



