268 Introduction to Botany. 



spores from the old sporangia over all sides of it, and keep 

 it in a moist atmosphere under a bell jar. When the 

 sporangia appear, note whether they all stand upright, or 

 whether the direction taken by them bears a definite 

 relation to the surface of the bread. Expose them to the 

 light so that they will be illuminated on one side more than 

 on another, and note whether the direction taken by the 

 stems which bear the sporangia is affected in any way. 



163. Examine the surface of a rusted leaf of wheat, 

 oats, or any of the wild grasses. Does the rust appear 

 on the veins or between them .■' Examine with a lens and 

 note whether the epidermis of the leaf has been broken by 

 the rust. Can any growths not belonging to the leaf be 

 seen .'' 



164. Make thin sections of the leaf across the rusted 

 spots, and mount under a coverglass in a drop of water. 

 If the leaf is dry, soak it for a few hours in water before 

 sectioning. The section of the leaf should be so thin that 

 the spores of the rust and the cells of the leaf immediately 

 beneath may readily be seen. The parts may be rendered 

 more transparent by mounting the section in a saturated 

 solution of chloral hydrate. Notice the course of the 

 thread-Hke part of the rust which penetrates the interior of 

 the leaf. 



165. Does the rust appear to produce any serious 

 mechanical injury to the tissues of the leaf.'' In what ways 

 is the injury to the plant probably produced.' Does the 

 rust appear to have any means of manufacturing its own 

 food independently of the plant on which it is growing .'' 

 What have you observed in regard to the ravages of rust in 

 wheat fields, etc. .' 



166. Examine a toadstool growing in the woods or 

 pasture. Dig away the soil carefully at its base to see 



