58 PRACTICAL COURSE IN BOTANY 



for instance, we have bony tissue and muscular tissue in 

 animals ; that is, tissue made of bone substance and muscle 

 substance and doing the work of bone and muscle respec- 

 tively. Likewise in plants, we have strengthening tissue 

 made up of hard, thick-walled cells, serving mainly for pur- 

 poses of mechanical support, and vascular tissue, made up of 

 conducting vessels for conveying sap — and so on, for every 

 separate function. 



Practical Questions 



1. Wh}' do raspberries and strawberries have a flabby, wilted look if 

 sugar has been put on them too long before they are served ? (7, 56.) 



2. Where has the juice gone ? What caused it to go out of the berries ? 

 (56, 59.) 



3. Is a knowledge of the principles governing osmosis of any practical 

 use to the housekeeper ? 



4. Why cannot roots absorb water as freely in winter as in summer? 

 (Suggestion : which is the heavier, cold or warm water ? ) 



5. Why does fertilizing too heavily sometimes injure a crop? (59.) 



6. Do you see any apparent contradiction between the action of plas- 

 molysis and the selective power of protoplasm ? Can you reconcile it ? 



7. If a piece of beet that has been frozen is placed in water it will be- 

 have just as the slice of boiled beet did in Exp. 40; explain. (58, 59.) 



II. MINERAL NUTRIMENTS ABSORBED BY PLANTS 



Material. — A dozen or two each of different kinds of seeds and grains. 

 A small portion from a growing shoot of a woody and a herbaceous land 

 plant, and of some kind of succulent water or marsh plant, such as arrow 

 grass iSagittaria), water plantain, etc. 



Appliances. — A pair of scales ; a lamp, stove, or other means of burn- 

 ing away the perishable parts of the specimens to be studied. 



Experiment 41. — Do the tissues of plants contain mineral 

 MATTER ? — Take about a dozen each of grains and seeds of different kinds, 

 weigh each kind separately, and then dry them at a high temperature, but 

 not high enough to scorch or burn them. After they have become perfectly 

 dry, Aveigh them again. What proportion of the different seeds was water, 

 as indicated by their loss of weight in drying? 



Burn all the solid part that remains, and then weigh the ash. What 

 proportion of each kind of seed was of incombustible material? What 

 proportion of the solid material was destroyed by combustion ? 



