PHYSIOLOGICAL BOTANY. 239 



on the chemical peculiarities of the vegetable cell, first from 

 Payer), he having previously made his excellent observa- 

 tions on Starch. The whole of these investigations were 

 published in 1842, in his ' Memoires sur les Developpe- 

 mens des Vegetaux/ He first instituted his experiments 

 upon the cellular tissue, which consists of little more than 

 membrane; this was taken from very young parts, e. g. the 

 ovule of the almond, pear, and apple tree, and of Heli- 

 anthus annum ; the delicate membranes formed upon the 

 coagulated drops of fluid which exude from the sections 

 of the vessels of the cucumber, also upon the pith of 

 young shoots of Samhucus nigra, cotton-wool after a first 

 and second purification, and the spongioles of roots, and 

 the pith of Aescliynomene paludosa (rice-paper). All these 

 substances were repeatedly treated with dilute hydro- 

 chloric acid and ammonia, washed with water before each 

 repetition of the process, and lastly exhausted with 

 alcohol and ether. They were then strongly dried, pow- 

 dered as far as possible, and then burnt with oxide of 

 copper. He found, as the result of the elementary analysis, 

 the composition C 24 H 23 O 3 , which is isomeric with starch. 

 He then gives a simple, direct experiment, by which 

 cellular membrane may be recognised under the mi- 

 croscope. A small section, e. g. of rice-paper, is placed 

 under the microscope in a drop of water; one or two 

 drops of an aqueous solution of iodine are then added, 

 which produce a pale-yellow colour ; and lastly, a drop of 

 concentrated sulphuric acid. The membrane is then first 

 coloured blue, and is finally wholly dissolved, so that 

 only yellow traces of the matters which were contained in 

 the membrane remain. A better method than this one 

 of Payen's, is to place the section for microscopic exami- 

 nation in a drop of water, then to add a drop of nitric or 

 hydrochloric acid ; to let the whole remain for about two 

 minutes, then to wash the section with water, and to 

 colour it with tincture of iodine. The membrane itself 

 now appears perfectly colourless ; sometimes it is slightly 

 bluish here and there, from a portion of starch which is 

 dissolved, and all the foreign matters are rendered deep 



