22 APPARATUS AND METHODS. 



obtained, consisting of a ring of glass with two glass tubes 

 annealed to it on opposite sides, and fitted up simply 

 cement one of the ground edges of the ring to a glass slide 

 with balsam. Lay the cover with the hanging drop on 

 the upper edge of the ring, smeared with vaseline to make 

 the chamber air- tight ; gases can be led through the cham- 

 ber, and therefore made to penetrate the specimen. 



20. Apparatus for Plant Physiology. Apart from 

 expensive " precision apparatus," made for research pur- 

 poses, apparatus for Plant Physiology may be either 

 (1) Normal or Standard Apparatus, made specially for 

 its particular purpose, giving quantitative results of ap- 

 proximate accuracy, and obtainable ready made from 

 supply firms who specialise in this kind of apparatus ; 

 or (2) Adapted Apparatus, made up carefully from various 

 appliances and articles sold for work in Chemistry and 

 Physics, these being altered to suit the special purpose, 

 giving qualitatively correct results and therefore serving 

 for elementary work and also in many cases for advanced 

 work in Plant Physiology ; or (3) Makeshift Apparatus, 

 put together from common appliances for temporary pur- 

 poses, giving only crudely qualitative results, and only 

 justifiable in most cases in a Nature Study Course. We 

 need only consider here the Normal and the Adapted 

 Apparatus. 



21. Normal Apparatus. The best set of apparatus of 

 this kind is that supplied by the Bausch and Lomb Optical 

 Company, from the designs of Professor G-anong. Various 

 pieces of the Ganong Apparatus are mentioned and illus- 

 trated in this book for full descriptions reference may 

 be made to the Company's catalogues and to Professor 

 G-anong's Plant Physiology. 



22. Adapted Apparatus. Much useful information 

 on the fitting up of apparatus in general is given in works 

 on Practical Chemistry (see Preface). The Chemical 

 Catalogue issued by Messrs. Baird and Tatlock should 

 be consulted for particulars of the various articles and 



