LABORATORY STUDIES 101 



It may be demonstrated by treating with dilute osmic acid 

 solution which turns fats black, or with alkannin solution, which 

 stains the fat drops red. 



(i) Place a geranium (Pelargonium) plant in the light for 

 several hours until starch has been produced in quantity in the 

 leaves. On two or three leaves cut one or two of the main 

 radial veins leaving the other veins intact. Cover the whole 

 plant loosely with a bell jar to prevent these injured leaves from 

 drying out too much and place in the dark for from twelve to 

 twenty hours. Treat these leaves with alcohol and iodine 

 solution as in (/) to determine the location of the starch. It 

 will be found to have disappeared except from the portions 

 bordering on the cut veins, showing that it is through these 

 veins (vascular bundles) that the carbohydrates are transported. 



(j) Reserve protein in the form of aleuron in the seeds of 

 beans, peas, etc., was studied in connection with cell inclusions 

 (paragraph 24). It will be worth while to repeat these 

 observations. 



(&) Examine one of the powdery mildews (Erysiphaceae) as 

 an example of a hysterophytic lower plant that obtains its 

 food from living plants (i.e. is parasitic). Take a bit of infected 

 leaf and moisten with alcohol, then mount in water or dilute 

 potassium hydrate solution with the infected side uppermost. 

 By careful focusing the filaments of the fungus may be dis- 

 tinguished and here and there may be seen the haustoria 

 ("suckers") which are sent into the epidermal cells of the 

 leaf. Better developed haustoria can sometimes be found on 

 making cross-sections of leaves or stems affected by downy 

 mildew (Peronosporaceae) or white rust (Albugo). In these 

 cases the whole fungus except certain reproductive parts is 

 within the host plant, growing intercellularly and sending well 

 developed haustoria into the cells between which it passes. 

 In both cases note the lack of chlorophyll in the fungus. 



(0 Examine a dodder plant (Cuscuta) as an example of a 

 higher plant that is parasitic. No leaves are to be found and 

 in most cases no chlorophyll, and the plant carries on no 

 photosynthesis. The original root which penetrated the soil 

 dies as soon as the plant has attached itself to its host or even 

 before. Note the roots by which it obtains its food from the 

 host. Sections of the stem will reveal vascular bundles, epi- 

 dermis, etc., but usually no chlorophyll-bearing cells. 



