SPEEMAPHYTES. 



145 



a solution of common sugar in water : about fifteen per cent of sugar is the 

 best. A very good plant for this purpose is the sweet pea, whose pollen 

 germinates very rapidly, especially in warm weather. The spores may be 

 sown in a little of the sugar solution 

 in any convenient vessel, or in a hang- 

 ing drop suspended in a moist cham- 

 ber, as described for germinating 

 the spores of the slime moulds. The 

 tube begins to develop within a few 

 minutes after the spores are placed 

 in the solution, and within an hour 

 or so will have reached a considerable 

 length. Each spore has two nuclei, 

 but they are less evident here than in 

 some other forms (Fig. 79). 



FIG. 80. Germinating pollen spores 

 of the sweet pea, x 200. 



The upper part of the pistil 

 is variously modified, having 

 either little papillae which hold 

 the pollen spores, or are viscid. 



In either case the spores germinate when placed upon this 

 receptive part (stigma) of the pistil, and send their tubes 

 down through the tissues of the pistil until they reach the 

 ovules, which are fertilized much as in the gymnosperms. 



The effect of fertilization extends beyond the ovule, the 

 ovary and often other parts of the flower being affected, en- 

 larging and often becoming bright-colored and juicy, forming 

 the various fruits of the angiosperms. These fruits when ripe 

 may be either dry, as in the case of grains of various kinds, 

 beans, peas, etc. ; or the ripe fruit may be juicy, serving in this 

 way to attract animals of many kinds which feed on the juicy 

 pulp, and leave the hard seeds uninjured, thus helping to distrib- 

 ute them. Common examples of these fleshy fruits are offered 

 by the berries of many plants ; apples, melons, cherries, etc., 

 are also familiar examples. 



The seeds differ a good deal both in regard to size and the de- 

 gree to which the embryo is developed at the time the seed ripens. 



