6 INTBODUCTION. 



To render tissues transparent they may be soaked in a dilute 

 solution of caustic potash for a few minutes. If by this means 

 made too transparent, the tissue should be immersed in a dilute 

 solution of alum or of hydrochloric acid. 



It is very instructive to apply chemical reagents of various kinds 

 to the objects lying in water upon the microscopic slide. Dilute 

 sulphuric acid is often useful to coagulate protoplasmic structures 

 and to clear delicate tissues ; when this is added first, and after- 

 wards solution of iodine, the younger cellular structures turn blue, 

 while the older ones become deep yellow. Iodine alone colours 

 starch-grains blue. Sugar and nitric acid colour the protoplasmic 

 structures red. These reagents may be applied by means of 

 dropping from a glass rod or fine tube. It is often advantageous 

 to soak the sections for some hours in a solution of pure carmine 

 in ammonia diluted with water. The nuclei and cell-contents 

 become tinged with the carmine, and can thus be more readily 

 distinguished from the cell-wall. More particular reference will 

 be made to them in the chapters on Anatomy. Microscopic pre- 

 parations of soft vegetable structures are best preserved in 

 glycerine or strong solution of calcium chloride. Some objects 

 are advantageously mounted in Canada balsam ; these must be well 

 dried first, and, for a few days previously to mounting, should be 

 soaked in spirits of turpentine. Those who desire to obtain 

 minute instructions on the manipulations necessary for the study 

 of Vegetable Anatomy, may consult Schacht's ' Microscope,' trans- 

 lated by Currey, or the articles on these subjects in the ' Micro- 

 graphic Dictionary/ 



In physiological investigation various pieces of philosophical ap- 

 paratus are requisite. It is also often necessary in studying the 

 life-history of plants, especially the lower ones, to grow them under 

 different conditions and to watch them in their several stages. 

 Eor these purposes special appliances and chemical solutions are 

 needed. 



Lastly the student must remember that Botany is not an " exact" 

 science. Rarely, if ever, can a definition be framed in any branch of 

 natural history which is not subject to frequent and considerable 

 exception. These exceptions arise from the natural variations 

 which occur in all living organisms, either in accordance with 

 existing circumstances or as hereditary tendencies. Again, it must 

 be borne in mind that Botany is a progressive science, and there- 

 fore that the language and terminology in general use is not 

 always strictly accurate according to the most advanced state of 

 science ; hence many of the terms have to be taken in an arbitrary 

 or in a conventional sense. 



