246 



PRACTICAL COURSE IN BOTANY 



360 



Figs. 360, 361. — Protection of pollen in the 

 thistle: 360, position at night, or during wet 

 weather ; 361, position in sunshine. 



ment by turning the pot bottom upwards so that the flowering axis will 

 point downwards. This can be done by inclosing the pot in a bag of strong 

 cheesecloth, with the string tied loosely but firmly around the foot of the 

 stem to prevent the contents from falling out, and suspending the whole 

 bottom upwards. In making these experiments, use flowers that grow 

 in a long cluster, or raceme, and hold the main axis in a vertical position 

 by tying or weighting it down. Watch the behavior of the individual 

 flowers. Arrange another pot containing the same kind of plant, in the 



same way, and suspend one 

 361 in a dark place, keeping the 



other in the light. Does the 

 same movement take place in 

 both? Is it in response to 

 light, or to gravity ? 



280. Means of pro- 

 tection. — Where plants 

 have adapted them- 

 selves to insect polli- 

 nation, it is, of course, important to shut out intruders that 

 would not make good carriers. In general, small, creeping 

 things, like ants and ^r^ -^ 



plant lice, are not such A' '/ ' 



efficient pollen bearers 

 as winged insects, and 

 hence the various de- 

 vices, such as hairs, 

 scales, and constric- 

 tions, at the throat of 

 the corolla, by means 

 of which their access to 

 the pollen is prohibited. 

 To this class of adapta- 

 tions belong the hairy 

 filaments of the spider- 

 wort, the sticky ring 

 about the peduncles of weather. 



the catchfly, the swollen lips of the snapdragon, the scales or 

 hairs in the throat of the hound's-tongue, the velvet petals 



363 



Figs. 362, 363. — A bell flower : 362, position 

 in daylight ; 363, position at night, or during wet 



