the Nitrogenous Matter of Plants. 39 



with that of the nucleus, though of greater transparency. To 

 view this structure better, the rays of light should fall on the 

 object in a direction parallel to their course, whether it be ordi- 

 nary daylight or artificial light. It will further appear that the 

 diameter of these canals is often greatly reduced, and that the 

 fluid circulating through them carries along with it only trans- 

 parent granules of very great tenuity. Now, the existence of 

 such canals within the cell-cavity has always been regarded by 

 the majority of botanists as improbable ; and taking this opinion 

 in connexion with the minuteness of the phenomenon itself, it is 

 easily conceivable that the structures just recorded have escaped 

 the researches of micrographers. However, when the investigator 

 has been made acquainted with these phenomena, it is not diffi- 

 cult to demonstrate them, and this even in cells of medium 

 dimensions, provided they are sufficiently transparent and ex- 

 amined with adequate care and patience. To this end, it is 

 enough to moisten the preparation without soaking it with water, 

 to carefully avoid the presence of air which may adhere to the 

 surface, and after covering it with the glass cover, to examine it 

 assiduously and under those conditions with regard to tempera- 

 ture above pointed out. Should the canals not show themselves, 

 gentle compression may be exercised on the preparation, and then 

 the examination be renewed; for by this process the canals are 

 separated and made to stand out from the cell-wall, in the centre 

 of its cavity, where they display themselves and their anastomoses. 

 It is much preferable to make out the existence of these canals 

 without the aid of reagents; but they may be made more evident 

 by the addition of a solution of iodine in iodide of potassium, 

 which gives them a clear yellow or a reddish-brown colour, as it 

 does to the nucleus. But this reagent, though preferable to 

 alcohol or to the aqueous solution of iodine, does not afford a 

 faithful image of the phenomenon, for it slightly contracts the 

 component matter of the canals and deforms it. Besides, before 

 the manifestation of the colour, there is greater or less delay, 

 according to the condition of the fluid in circulation. It is 

 therefore most important, when it is wished to make a critical 

 examination, to abstain from the employment of this reagent, 

 and, indeed, of any other; for, as we shall very soon discover, 

 their vital movements, which such reagents destroy, are the most 

 important of all their properties, and to be studied with the 

 greatest advantage. 



The canals existing in a cell derived from elsewhere than the 

 hairs of plants may have various origins ; but I shall first point 

 out the characters of such as are in connexion with the nucleus, 

 distinguishing those peculiarities in which they differ from the 

 last-named organ. These canals, being constituted by the mem- 



