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. 
(t) 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 (f) 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. 
(k) 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. 
(1) 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. 
