158 ACTION OF AMMONIUM MOLYBDATE, ETC., 



quite unable to explain the nature of the chemical change brought 

 about — some of my friends suggesting that it is due to the pre- 

 sence of phosphorus in some form of combination ; but I am 

 inclined to regard it as a form of oxydation of the cell-contents. 

 I give the results of my observations on 120 genera, placing them 

 in their ordinal relation to each other, the sign x signifying a 

 decided result or reaction ; — meaning a moderate or partial ; and 

 o, no change worth recording. 



The plan I have adopted is as follows : — I obtain the cuticle of 

 a leaf, preferably from the under surface, by peeling it off, or 

 shaving it off with a lancet or sharp knife. This last can usually 

 be effected without much difficulty ; but when the upper cuticle is 

 required, then the process of cutting becomes more difficult. If 

 the leaf is folded over the finger and held firmly, the lancet will 

 slice off a thick and thin portion sufficient for observation. I 

 then place the cuticle, with its surface, on the slide, the cut por- 

 tion uppermost, and applying water, I add a small drop of 

 Ammonium Molybdate solution, and watch the effect. 



Usually, in a short space of time, one notices the effect of the 

 reagents by the colour produced in some of the cells, varying from 

 a pale lemon-yellow to a deep orange tint. This colouration 

 usually first appears in the cells of the epiderm, and spreads to the 

 hypoderm, or next layer of cells, and invades the cells of the vas- 

 cular portion of the leaf If there is no reaction, or one that 

 appears uncertain, I add a drop of the Sulpho-Cyanide solution, 

 and often the colour deepens. When I wish to preserve the spe- 

 cimen in Canada Balsam, I gradually introduce diluted, and then 

 stronger alcohol, which seems to precipitate the salt in a resinous- 

 looking cloud, and which I remove by further addition of alcohol, 

 and removing the specimen to a clean slide, drop on the Canada 

 Balsam, without heat if possible. In some cases, I first alcoholise 

 the specimen to be examined, and then add the Molybdate, and I 

 am inclined to think the alcohol acts on some of the cells as to 

 their chemical character, and that when the Molybdate takes 

 effect, it does so only on those cells which have escaped the action 

 of the alcohol, as the coloured cells appear to be fewer compared 

 with other specimens of the same leaf differently treated. 



I consider it will be necessary to go over these experiments at 



