and Exfoliation in the Roots of Plants. 203 



The radicle of wheat {Triticum sativum) when it originates in 

 the ordinary conditions of the atmosphere, presents itself in the 

 form of a cylinder conical at its apex, and in the centre of this 

 latter region exhibits a portion of a sphere formed of quadrilateral 

 cells, which, coloured of an amber tint, taken as a whole, differ di- 

 stinctly from the more elongated and colourless cells which cover 

 them. The former constitute what, for the better comprehension 

 of the facts, we will call the summit of the radical axis, and 

 and the latter that of the cortical layer. 



Taken in these conditions, and at the outset of the germina- 

 tion, all the cells of the cortical layer, including those of its 

 apex, are smooth and coherent, and the most external are longer 

 than those which they immediately cover. 



In proportion as the organ grows, it is observed that the epi- 

 dermal cells, which are of larger size according as they are placed 

 nearer to the base of the radicle, contain an animal matter which 

 is coloured pale rose by deutonitrate of mercury, and dark brown 

 by iodized iodide of potassium. This substance, which contains 

 extremely fine granules, accumulates in the middle region of the 

 cells into a little heap, above which the wall of the cells becomes 

 rounded externally in the form of a slight hernia, into the cavity 

 of which the same matter passes ; and in proportion as it accu- 

 mulates there, this appendix becomes developed, until it acquires 

 a length equal to twice or three times the diameter of the radicle ; 

 so that each epidermal cell with its absorbing appendix (radical 

 hair, A. H.) presents the form of a cross with an excessively long 

 shaft. 



It is not possible to trace the mechanism by which this sub- 

 stance determines the elongation of a portion of the wall of the 

 cell into this appendix; but we may conjecture that, as the 

 essential agent of all cellular formations, it is this which secretes 

 and coordinates the materials. 



In proportion as the radicle is developed, and usually when it 

 has attained a length of 1 to 3 centimetres, it may be observed 

 that its apex is swollen, and has assumed the form of a tear. 

 This region, which is viscid to the touch, readily becomes soft- 

 ened when immersed in water, communicating to it a consistence 

 like that of white of egg, and a very marked sweet taste. 



The radical extremities of 500 grammes of wheat, immersed in 

 distilled water, gave a solution which, when heated to 140° F., pre- 

 sented flocculent coagula of azotized matter (caseine, albumen) ; 

 and when this matter was separated, and an excess of alcohol of 

 0*815 spec. grav. added to the liquid, there was produced a pulve- 

 rulent deposit in a grumous mass of pasty consistence and sweet 

 taste, formed of a mixture of dextrine and sugar. The substance 

 precipitated in a state of powder, saccharified starch in the same 



