108 PLANT PHYSIOLOGY 



hours to determine in what segment so marked the most 

 rapid growth occurs. It must be remembered that tliis zone 

 of most rapid growth is rapidlj^ passing down the root all 

 the time, keeping about the same distance back from the root 

 tip, so that the marked root must not be left too long before 

 examination or the conclusions will be faulty. 



(c) Attach the thread of an auxanometcr (instrument for 

 measuring growth) to the tip of a leaf just growing out of an 

 onion or hj-acinth bulb or to the tip of the flower scape of such 

 a plant, or just below the cotyledons of a sunflower seedHng. 



If possible have the plant in a situation where 

 it is almost equally lighted from all directions. 

 If the instrument is not self-recording readings 

 should be made every one or two hours during 

 the day and night. If the records are automat- 

 ically made the readings need not be taken during 

 the course of the experiment but the records can 

 be studied afterward. So far as possible keep the 

 nomete/Sr* temperature constant. Interesting results may 

 be obtained by varying the temperature while 

 keeping the intensity of the light the same or bj^ varjdng 

 the hght with constant temperature. The effect of keeping 

 the soil very wet and very dry may also be compared. 



(d) Observe a potato that has started to grow in a dark 

 corner of a cellar and compare its growth with that from a tuber 

 that has been grown in full hght. 



(e) Place potted plants under bell jars as follows: (1) clear 

 white glass, (2) double bell jar with space filled with saturated 

 K2Cr207 solution, (3) double jar with space filled with saturated 

 cuprammonia solution. Compare the growth. Note also the 

 differences in the color and development of the leaves. The 

 cuprammonia solution is prepared by carefully adding to a 

 copper sulphate solution sufficient ammonia to precipitate all of 

 the copper as copper hydroxide but not adding enough ammonia 

 to redissolve the precipitate. Filter and wash the precipitate 

 and then dissolve it in strong ammonia using only enough of 

 the latter to completely dissolve it. This must not be done 

 on the filter paper as the solution thus formed dissolves cellulose. 



(/) The rate of growth under normal conditions can be meas- 

 ured by an auxanometer or with a horizontal microscope or in 

 the case of rapidly growing plants, such as Indian corn, morn- 



