218 



THE AMERICAN 



successively to different cliemical reactions 

 which eti'ecl :i desf ruction of all forciuii mnttei-s 

 adherent to tlic membrane in (luesiion. 



Tliere is no difficulty in sliowiuji' you tliis part 

 of tlie veuetable cell. Take a potato, cut it, and 

 tal<c from the cut surface a very tliiu slice on an 

 object-glass ; cover it with a covering- glass plate, 

 and add a drop of water. You ivill i-emark on 

 tlie edges of the slice many cells, in some parts 

 only a poi-tion. rent, lacerated, and out of con- 

 nection with llic adjaci'iif cells. 



If you liavc any dciubl of that being a cellulose 

 membrane, you add some solution of Iodine. 

 Instantly you see the starch in the cell colored a 

 deep blue. The membrane remains transparent, 

 white as before. Add a drop of sulphuric acid 

 and you will see, after a wliile, the membrane 

 also take a blue hue, but not so intense by far 

 as the starch bodies near by. Tlic i>ur(s near the 

 corner where you let enter the -nliihuiic mid 

 are colored first, and the color advances gradu- 

 ally in tlie other dii'ection. 



I made some tine slices of the root of Valeriana 

 offieiuaUs. In putting them between the glass 

 plates I could not disiinguisli any cellulose mem- 

 brane, or any indication of it. It was because 

 the salts spread through the cells, and the in- 

 ci'ustations in their walls rendered the membrane 

 opaque. In boiling the preparation, the water 

 took so much of the soluble salts away that the 

 cellulose membranes could be seen ver)^ clearly. 

 This boiling can be performed in any vessel ; but 

 for our purixise it suffices to add some' drops of 

 water to the object glass, and hold it for an in- 

 stant over the alcohol lamp. The jumping- up 

 and down of the covering glass-plate denotes 

 that there is steam formed, whose expansive 

 power is utilized in the locomotive. 



Now the cellulose membrane is degarnisbed 

 enough to be observed, and we can (r\ I lie same 

 exp<-riment with the iodine and sulpliui-ic acid 

 as alluded to before. It is inditl'erent wliicli of 

 tlie two yon add first. I boiled the valerian root 

 in water containing a few drops of sulphuric 

 acid, and the membrane grew free to a greater 

 exti-nl. because the sulphuric acid is a strong- 

 dissolvent for organic as well as for inorganic 

 salts. When you put this slice under the micro- 

 scope, and add a droy) or two of iodine solution, 

 you remark easily the growing of the blue color 

 at tlie margins before wliite. I tried the same 

 experimeni on a fungus which luxuriated upon 

 an animal mailer, but witli a negative result. A 

 fungus growing in a sugary solution should be 

 carefully washed, because the sugar, being trans- 

 formed by suljihuric acid into dextrine, can take 



membrane of these two vegetables (potato and 

 val<Tian) i- sniootli. williout any pores. 



The -ncce"i\( coloring of the contents of an 

 iiiteg<T cell fnnii tlie side tVom which the reactive 

 comes, demonstrates that it is only by (he law of 

 Osmose, and not through pores or other boles in 

 the wall that the coloring is eflected. 



We find often at the inside of the cuticle of 

 cellulose, layers of different form, thickness and 

 arrangement. These layers have sometimes the 

 form of a circle, sometimes of a si>ii-al. sonielimes 

 of large dejiosits covering more or less llie entire 

 surface of the cell. 



When the cell contains one or more rings, it is 

 called the cellula [Fig. i:!i).] 



annulifera, or; 

 ring-bearing cell. 

 We find these 

 mixed with spi- \'S^~-^=^U*i5^^\l*^^^f==*^^l 



rals in a trans- Transverse cut of Hyacinth leaf . 



verse cut of a leaf of Hyacinth ( Fig. 136). When the 

 two ends do not grow together, then the layer 

 inside the cell takes the form of a spiral ; this 

 spiral can run from the left to the right, or from 

 the right to the left. The cells containing the 

 spiral are called fibre cells, when the fibres are 

 clearly separable from the cell wall. A trans- 

 verse cut of Hyacinth shows very distinctly these 

 spirals. And you can also distinguish some 

 fibres running from I'ight to left, and one running 

 in the contrary direction. The same can be ob- 

 sei-ved in a few cells out of the pith of Geranium. 



[Pig. 137.) 



Pith of Geranium, 



In this example I bad rent the spiral out of the 

 cell, and so I could study it more closely. I found 

 it an ehistic substance without bole in the in- 

 terior, the breadth being everywhere the same. 

 In one part I distinguished that the fibre-ribbon 

 was split in the middle (Fig. 1:17, ua) but soon 

 coming together again, leaving a kind of button- 

 hole. 



In the fibrous cell adjacent (Fig. 137, b) I re- 

 marked that, iit the borders of the i^ell where t\\Q 

 fibi-e-ribbon passed from above to below, there 

 was a little while spacu' (Fig. 137, c). the eflect 

 of the interference of the light. I followed the 



