26 



there can be discovered by the microscope anything in the arrange- 

 ment and nature of the tissues of those parts which exhibit the above 

 alterations and separation of their several portions, that will account 

 for these changes satisfactorily. 



In plants like mosses or other vegetables which merely expand and 

 contract by the application of moisture, without disturbing the rela- 

 tion the several parts bear to each other, nothing can be seen in such 

 beyond the ordinary character of cellular tissue, and in all probability 

 the avidity for water in these plants depends upon some different che- 

 mical characters of the tissues themselves, when contrasted with cel- 

 lular tissue not so hygroscopic; this power of absorption being always 

 most in new, and in those tissues which are devoid of deposits. 



When however other examples are examined where evident dis- 

 placement or separation of parts obtains, and this always in the same 

 direction and attended always with like results, then it can be disco- 

 vered that not only is the tissue more hygroscopic at that part, but the 

 arrangement is such as to ensure the effect nature has intended. Let 

 us take, for example, the capsule of some plant of the order Caryo- 

 phyliea, as Cerastiutn, and it will be found that when that organ ap- 

 proaches maturity, the apex, which was pointed and entire, will 

 open by splitting into five equal valves, which curl outwards, making 

 one complete coil, and always in the same direction ; by the applica- 

 tion of moisture the valves will resume their original position, and 

 when dry take on the curled form again. 



If one of these valves be examined it will be found to be thin and 

 diaphanous where it forms part of the body of the capsule, but where 

 it is hygroscopic it is horny and opaque. When a section taken from 

 the edge of the valve or curled part longitudinally is examined by the 

 microscope, it will be found that the tissues will be different on the 

 exterior and internal surfaces, both however cellular ; but the inner 

 layer, or the cells of the convex border, are of different dimensions 

 from the outer, being neither so large nor having so thick walls, (though 

 they are thicker than ordinaiy cells) ; whilst those of the outer layer 

 are almost solid, and the only cavity they have is indicated by thin 

 spaces between a series of lines, the chief one of which is in the di- 

 rection of the longer axis of the cell, the others connected to it at 

 right angles. These cells are of most curious structure, and form an 

 interesting object for the vegetable anatomist. 



In this arrangement of parts it must be evident that by the shrink- 

 ing of the tissues of the seed-vessel by loss of moisture, there will 

 occur unequal contraction, and that side will be curved which con- 



