Januaey 9, 1914] 



SCIENCE 



67 



that the single one of the pro-transformism 

 arguments of the writer in Le Pays which 

 remains in his memory is, that the best geolo- 

 gists of the United States believe in evolution. 

 The Abbe justly remarks that the argument 

 does not seem to him overwhelming. For, he 

 adds, they and even most geologists of the Eng- 

 lish language and protestant faith are parti- 

 sans of evolution because of their lack of 

 philosophic and religious instruction. 



V. L. K. 

 Stanford University, Cal. 



a simple apparatus foe illustrating photo- 

 synthesis 



The use of experiments, illustrating the 

 various physiological processes in plants, are 

 coming more and more into use in connection 

 with the teaching of elementary botany in the 

 secondary schools. Unfortunately the funds 

 available for the purchase of apparatus are so 

 limited in many of these schools that the 

 teacher has to resort to the method of making 

 the various experiments before the class, while 

 the students make notes on the results, etc., to 

 be v^itten up in their laboratory notebooks 

 later. Such a method as this is very good if 

 nothing better is available, but of course the 

 best results are obtained by the students them- 

 selves making as many of the experiments as 

 possible. I devised the following simple appa- 

 ratus for illustrating the necessity of carbon 

 dioxide and light in photosynthesis. Since it 

 has worked with success, I thought that a 

 short account of it might be justified. 



Ordinary bottle corks, about 2 cm. in diam- 

 eter, and 1 cm. thick, should each have a hole 

 cut through the flat side with a large cork 

 borer. The holes should be about 1.5 cm. in 

 diameter. Through one side of each of the 

 cork rings thus formed, a small hole should be 

 made for ventilating purposes. The large hole 

 in each ring should now be covered on one 

 side by cementing on a small piece of mica, or, 

 if mica is not available, small round cover 

 glasses will do, but will require more careful 

 handling subsequently as the glass breaks 

 more easily than the mica. A sufficient num- 

 ber of these discs should be made to provide 



each student with six of them, two of which 

 should be blackened to exclude the light. 



In order to perform the experiment success- 

 fully a bright day should be selected, and only 

 such plants should be used as have the sto- 

 mata on the lower sides of the leaves. Plants 

 with the stomata on both surfaces can be 

 used, however, provided that the upper sur- 

 faces of the leaves used in the experiment are 

 greased with cocoa butter or vaseline. The 

 plant should be left in the dark long enough 

 for the starch to be removed from the leaves 

 before the experiment is started. 



The cork discs, which have just been de- 

 scribed, should be pinned to the leaves in 

 pairs, one on the upper surface, and another 

 on the lower surface opposite it so as to form 

 small enclosed chambers in each instance. 

 The blackened discs should constitute one pair 

 so as to form a dark chamber. In order to 

 exclude carbon dioxide the lower chamber of 

 one of the other pairs of discs should contain 

 small lumps of soda-lime, while the third pair 

 will serve as a control to show that the pres- 

 ence of the discs themselves does not interfere 

 with starch formation. 



After the plant has stood in the sunlight 

 for a few hours the leaves upon which the ex- 

 periment is made should be removed, boiled in 

 water, left in alcohol for a time and tested for 

 starch in the usual way. If the experiment 

 has been properly conducted, no starch will be 

 present where carbon dioxide and light have 

 been excluded, but it will be present in abun- 

 dance under the discs used as a control. 

 Groups of from two to four students can work 

 together if the class is large and the number 

 of discs limited. 



It has been found that rather large-leaved 

 plants with stiff petioles are better for use, in 

 which case one leaf is sufficient for the three 

 sets of discs. If plants with delicate leaves 

 are used the discs can be supported by bend- 

 ing short lengths of soft iron wire at right 

 angles near one end of each, and inserting the 

 bent end in the side of one of the discs in each 

 pair, while the other end of the wire is stuck 

 into the soil below. Alban Stewart 



TjNrvEBSiTY OP Wisconsin 



