16 



GoRHAM, on the Umbellifera. 



far better idea is gained, indeed, of the structure and real 

 appearances of any object by using the weakest power com- 

 patible with correct definition, than by a display with a 

 regular microscope, which sliows only small detached parts 

 prodigiously amplified. As microscopists, it is possible we 

 have paid too little attention to a large class of objects re- 

 quiring powers intermediate between those of the naked eye 

 and those of the highest magnifiers to make them visible. 



Instruments of low powers, though by far the most 

 amusing, and in many cases the most useful instruments also, 

 seem to have been quite neglected, while the higher powers 

 have been brought to the greatest perfection of which^ per- 

 haps, they are capable. 



It must be recollected, however, that the more we magnify 

 any object, the less we must be content to see of it, according 

 to the law of optics. 



A lower power, then, with a wide field, becomes a most 

 useful optical instrument for examining the structure of 

 leaves ; and if it be placed on a tripod, the proper focu.s may 

 be obtained once for all, and thus a large number of leaves 

 may be examined easily and expeditiously. 



It may be necessary to view the specimens either by trans- 

 mitted or by reflected light. If the greater spaces are to be 

 investigated, the glass should be held up before the window, 

 when the reticulations will be seen presenting a firm, trans- 

 parent, and often coloured netAvork, the colours diiferino- 

 from that of the leaf itself, and often conferring great beauty 

 and brilliancy iipon it. If, on the other hand, it is desirable 

 to notice the veins at the margin of the leaf, they will be seen 

 to the greatest advantage by holding the glass horizontally in 

 front of the window and placing a piece of white paper 

 underneath, so as so view them on a white ground. 



The anomaly of a marginal venation in a leaf to which I 

 am about to dn-cct attention will be better understood, and 

 more properly appreciated, I presume, if the ordinary modes 



