STUDIES OF SEEDS AND SEEDLINGS 9 



In the Four-o'clock remove the iutegUTiieuts, and separate embryo 

 and albumen carefully. 



Draw the food mass of Four-o'clock. Indicate by dotted lines the 

 natural position of the embryo. Use the hand lens ( x o). 



2. What substances constitute the food of the seedling ? The very 

 mimeroiis substances of which plants are composed are capalile of 

 being recognized by appropriate tests. A test consists of the treat- 

 ment of the tissues with certain chemicals. The success of the test 

 depends ujion observing some change of appearance, as of color, known 

 to be due to the action of the chemical employed upon the substance 

 foi' which search is Ijeing made. 



Test for starch. — Treat a piece of laundry starch with dilute iodine. 

 Note the color imparted. Starch alone receives this hue from this 

 reagent. Experiment upon the seeds supplied in order to determine 

 which contain starch, and in what parts the starch, if found, is lodged. 

 It may be necessary to pulverize or boil a part of the seed in some 

 cases. 



A second food material, of frequent occurrence in seeds. — Crush a 

 whole kernel of Castor Bean. If this is done with the fingers, the 

 characteristic feeling of the expressed lirpiid when the fingers are 

 rubbed together shows the nature of the food material in question. 

 Seeds of Flax and of Cotton may be cru.shed out with the flat of a 

 knife blade for the same suljstance. 



Other forms of reserve food mailer. — Several of these are not readily 

 discovered without chemical tests or microscopic examination. But a 

 form occurring in the seeds of a nninl)Pr of plants of considerable 

 economic importance is well seen in the date seed. Cut the "stone " 

 of a date in halves transversely. Examine with the hand lens the 

 small emiiryo lying crosswise of tlie seed. 



Xote the toughness of the main bulk of the seed. It is not gritty, 

 like the stone of a cherry, bnt hornlike. It is the albumen, dissolved 

 dnring germination and used for the support of the seedling. 



From the studies in Exercise II answer the question, AVhat provi- 

 sion is made in the seed, in the way of food, for the growth of tlie 

 seedling and its establishment as an independent individual? 



THE SEEDLING. GERMINATION 



Exercise III. What Internal Processes are Discoverable 

 AS THE Embryo Begins to Grow, and Growth Progresses? 



Experiment i. — Select seedlings of Bean in the first stages of germi- 

 nation, the caulicles coming into view. Remove the seed coats. Drop 

 a dozen of the denuded beans into a four-ounce or six-ounce bottle 

 tilled with water which has been recently boiled to drive off dissolved 

 air, and allowed to cool. 



