xii PHYSIOLOGY OF GROWTH AND MOVEMENT 155 



EXPT. 145. Obtain a well-developed Deadnettle and examine it. 

 Note 



(i) The leaves are crowded together at the base and apex ; between 

 these two regions they are further apart. 



(ii) The leaves are produced at the nodes in pairs ; where the inter- 

 nodes are long the leaves are a greater distance apart. 



(iii) That part of the stem where the internodes are longest were 

 produced during the grand period of growth. 



EXPT. 146. Sow a few seeds of the Indian Corn in a pot. Keep 

 the soil moist and warm, and exposed to light in a window. Measure 

 with a tape-measure both the growth in length and thickness of the 

 seedlings from time to time. Measure and record 



(i) The circumference of the plumule when it first appears above the 

 ground. 



(ii) The length of the plumule when it first appears above the 

 ground. 



(iii) Repeat the above measurements every day during the growth of 

 the plant. 



(iv) Preserve the record of the series of measurements for future 

 reference. 



EXPT. 147. Germinate a Bean seed, and when the radicle is well- 

 developed wash it. Measure off half an inch from the tip of the 

 radicle, and divide it into ten equal parts by marks with Indian ink. 

 Pass a fish hook through the seed, and suspend it to a cork in a bottle 

 which contains a little water. Examine at the end of twenty-four hours. 

 Note 



(i) The amount of growth. Measure from the tip of the radicle to 

 the mark nearest the base. 



(ii) The grand period of growth is well illustrated by the amount of 

 elongation between mark (3) near the tip and mark (4) from the base. 



(iii) The differences in the amount of growth in the different parts 

 of the root are due to the two zones of growth. The greatest amount of 

 elongation takes place in the zone where the cells are increasing 

 in size. 



Irritability. Living protoplasm possesses many properties, 

 but one of the most important is its power of responding to ex- 

 ternal stimuli. This property is called irritability or 

 sensitiveness. The response to these external agencies very 

 commonly produces movements. 



Growing organs possess the property of irritability to a far 

 greater extent than the older parts of plants. The irritability 

 of growing organs must be distinguished from the irritability 

 of mature organs. 



