The Microscope. 71 



condition of a simple cell or single elementary organ, from 

 which all take their start, through all their deviations and 

 complications, leading to a knowledge of the conditions of all 

 parts and at all periods, comes to our Lands as the process of 

 verification ; since, so far as we at present know, it is found that 

 the same changes and the same kinds of growth take place in 

 a similar manner in all plants, whether they be the principal 

 moments of life of a simple microscopic being, or subordinate and 

 passing phenomena in the life of the mighty giants of the tropical 

 forests whose periods of growth extend through centuries. 



The elementary organs of plants are too small to be distin- 

 guished singly by the naked eye. For their investigation, thei'e- 

 fore, it is necessary to have recourse to magnifying instruments ; 

 and hence the Microscope is one of the indispensable tools of the 

 physiologist. The value of microscopic observations and the 

 certainty belonging to them are no longer subjects of question 

 among scientific men ; but there still lingers perhaps among tlie 

 uninitiated some of that incredulity and suspicion which almost 

 always attaches at first to any contrivance for extending the reach 

 of the senses beyond the ordinary range. A little I'eflection, 

 however, is sufficient to show how groundless are the objections 

 usually urged as to the uncertainty and discrepancy of the state- 

 ments made by microscopic observers. In the first place the 

 microscope is a tool requiring delicate and skilful management, 

 and can no more be applied efficiently without practice and skill 

 than the turner's lathe. In itself, a well-made modern microscope 

 is a very perfect instrument, and the physiologist depends upon 

 it as the surveyor does upon his theodolite or the navigator on 

 his sextant. The optical principles upon which a microscope 

 are constructed are now sufficiently understood, and the work is 

 now so well executed, that in the majority of ordinary observa- 

 tions there is little danger of deception, except from tlie want of 

 care in preparing the objects observed. 



The utility and mode of action of the instrument may be very 

 simply explained. With the naked eye we see objects clearly 

 only witliin a certain range, not beyond a certain distance, and 

 also not within a certain distance. The absolute distances vary 

 with different persons ; but any one may observe that if a piece 

 of printed paper is held before the eye, so that the letters are 

 clearly seen, ami it is then brought gradually very close to the 

 eye, the letters become confused, and all distinct vision is lost. 

 The eye, in fact, consists of a set of lenses (or wliat arecommonlv 

 called ' magnifying glasses ') capable of much adjustment, but 

 incapable of being adjusted so tliat objects almost close to the 

 eye can be seen. The rays of light from such ()I)jects arc not 



