PLANT PHT8I0L0QT. Ill 



(6) Select a symmetrically grown fuchsia, place it in a window, 

 and note the rapidity with which the leaves and stems turn toward 

 the light. 



(c) Germinate various seeds in a window, and observe the helio. 

 tropism of the seedlings. Young heet seedlings are very sensitive. 



(d) Grow a strawberry -geranium (Saxifraga sarmentosa) in a hang- 

 ing-basket or pot in a window, and observe that the dependent run- 

 ners bend away from the light. 



(e) Germinate seeds of cabbage, radish, parsley, or tomato, and 

 note carefully the position of the cotyledons during the day and 

 night. 



(/) Observe the sleeping state of wood-sorrel (Oxalis), clover, and 

 purslane. Then make careful notes of diurnal and nocturnal posi- 

 tions of the leaves of as many plants as possible. Where it is possi- 

 ble to do so it is recommended that photographs be taken of the 

 waking and sleeping states of plants. Careful sketches, at least, 

 should be made. 



191. Irritability. — Many parts of plants exhibit move- 

 ments as a result of physical contact with some object, 

 ror this sensitiveness to contact the term irritability has 

 been used. One of the best examples of this is the virell- 

 known "sensitive-plant" {Mimosa pudica, Fig. 189) whose 

 leaflets quickly assume a particular position when rudely 

 touched. A more remarkable example is the Venus's fly- 

 trap {Bionma muscipula. Fig. 169), in which each lobe of 

 the leaf has three sensitive hairs upon its upper surface; 

 and when these are touched the two halves of the leaf close 

 together quickly. Many stamens are sensitive to touch, as 

 in the barberry, portulaca, and purslane. 



192. The tendrils of many plants exhibit irritability, and 

 when touched by an object bend toward and eventually coil 

 around it. If after contact and some bending the tendril 

 be freed once more, it will soon straighten out as before, 

 and may be made to bend in the opposite direction by an- 

 other contact; and this may be repeated a number of times. 



Practical Studies.— (a) Grow a few sensitive-plants in pots for 



