12 EXPERIMENTAL PLANT PHYSIOLOGY. 



EXPERIMENT 13. 



NUTRITION OF BACTERIA AND RELATED FORMS. 



Make a solution of sugar in a cylinder and set in a warm room 

 for three days. A film or scum will be formed on the surface of 

 the liquid. Under a magnification of 600 diameters the scum will 

 be found to consist of an immense number of globular, cylindrical, 

 or spiral cells of Bacteria and other forms which obtain their food 

 from sugar and complex substances formed by other plants. 

 These organisms absorb food-material through their entire surface. 

 The spores of such plants are found floating in the air and develop 

 whenever they come in contact with food under proper conditions 

 of temperature. 



10. Physical Aspects of a Plant. — From a purely physical 

 point of view the plant may be regarded as a cylindrical 

 chamber whose walls are composed of membrane, and whose 

 contents consists of a large number of stable and unstable 

 compounds dissolved in water. At both ends of the cylinder 

 the surface is magnified, at the lower end in the roots and 

 root-hairs, and at the upper end in the leaves, to facilitate the 

 diffusion of gases and liquids. The body of the cylinder, the 

 stem, acts as a tubelike conductor between these surfaces. 

 The outer layer of the stem is not easily permeable by fluids. 



11. Diflfusion. — By diffusion is understood any exchange 

 which may take place between two fluids in contact either 

 directly or through a membrane. This latter exchange is 

 termed osmose. Diffusion takes place regardless of gravity 

 until the fluids are alike. Not all fluids are capable of osmose, 

 but only those which are imbibed by a membrane. The 

 rapidity of diffusion varies with the mobility of the fluids. 

 Stable compounds diffuse with more difficulty than water. 

 Concentrated solutions of these compounds increase in volume, 

 since they gain more water than they lose. They occur in the 

 root-hairs, and in consequence a large quantity of water is 

 taken up and forced into the root and upward in the stem. 



