and Laboratory Methods. 2233 



vals of five to eight minutes take out a few drops of the acid mixture with a glass 

 rod and test for starch with iodine. At intervals of ten minutes test for sugars 

 with Fehling's solution ; but before testing neutralize each sample with potas- 

 sium hydroxid, using litmus paper as an indicator of the neutral condition. 



To observe the action of diastase upon normal starch grains, place a small 

 amount of wheat starch and a few cubic centimeters of diastase solution in a 

 well covered dish. Acidify the mixture by the addition of a hydrochloric acid 

 so that it is about .05 per cent. acid. At the end of twenty-four and of forty- 

 eight hours examine microscopically to observe the corrosion of the individual 

 grains. 



X. CORRELATIONS BETWEEN DIFFERENT PARTS OF PLANTS. 



There is often manifested in the growth of new shoots an internal reciprocity 

 which has been termed the correlation of growth. These processes are espe- 

 cially induced by the mutilation of plants. One of the most convenient subjects 

 for this study is Willow or Poplar cuttings ; preferably they should be used in 

 the spring before the leaves start. Before placing the cuttings in the culture jars 

 they should be washed quickly in a weak solution of mercuric chlorid and rinsed 

 in distilled water, otherwise they are likely to become infested with fungi. 



1. Polarity of Stems, (A) Make five cuttings of similar length and fasten 

 them upright in a battery jar; allow the lower ends to dip about 1 cm. into 

 water in the bottom of the jar. The sides of the jar are to be lined with filter 

 paper and the jar is to be covered. Note the regularity with which leaves and 

 roots develop on the upper and lower ends respectively. 



(B) Make a preparation precisely similar to the preceding, except that the 

 shoots are to be inverted with their morphologically upper ends dipping into the 

 water. Note the marked polarity of the stems as shown in Fig. 9. 



(C) Five similar shoots are to be planted with the morphologically lower half 

 embedded in clean sand in a flower-crock which sets constantly in water. The 

 projecting ends of the shoots should be covered with a sheet of wet filter paper 

 and a bell-jar placed over all. The result is practically the same as (A). 



(D) A similar preparation to the foregoing is made, except that the morpho- 

 logically upper half of each cutting is embedded in the sand. Compare results 

 with (B). 



2. Formation of Roots and Leaves in Response to Injury by Girdling. The gird- 

 ling experiments give one an idea of the paths of water and of plastic material 

 in the stem. The results in each case are to be compared with No. 1 (A). 



(A) Make a preparation similar to No. 1 (A), cutting out in the center of 

 the stem a complete ring of bark 1 cm. in length. See that all of the bark and 

 phloem are removed, leaving only the wood beneath. 



(B) Make another preparation similar to the preceding, except that the bark 

 is removed one-third the distance from the lower end of each cutting, 



(C) Make a preparation similar to the foregoing, except that the bark is to 

 be removed one-third the distance from the upper end of each cutting. 



The resultant growth in such cuttings is shown in Fig. 10 ; roots are formed 

 where the downward flow of plastic material is stopped by the removal of the 



