18 SIZE OF CELLS. 



tree, for carrying off by evaporation all naoisture which may escape from 

 the cells, which may ooze out, or may be passed by exosmosic action j 

 and a little further consideration may lead to the conclusion that the 

 arrangement has been made, not to get rid of accidental leakage, but of 

 all moisture in excess of what is actually required after the sap has been 

 so elaborated as to fit it to minister to the nutriment of the tree. Be 

 this as it may, it is not unreasonable, but the reverse, to suppose that, 

 however compact the tissue or structure of the cell wall may be, there 

 may be, or that there must be, interstices between the molecules of 

 which it is composed. A drop of water falling upon a heap of fine 

 dust, or of powdered rosin, immediately draws around it a water- 

 proof covering of the material amongst which it has fallen, which, 

 though waterproof, is not airproof, and the enclosed waters may be 

 evaporated through the interstices of the investing covering. So may 

 it be with these, though on a scale infiuitesimally reduced. 



Professor Huxley, in a paper " On the Border Territory between 

 the Animal and Vegetable Kingdoms," which appeared in Macmillan's 

 Magazine for February 1876, citing some remarkable observations on 

 certain monads by Messrs Dalliuger and Drysdale, which were 

 embodied in two papers in the Monthly Microscopical Journal for 

 1873, speaking of certain granules, living embryos, remarks, — "The 

 authors whom I quote say that they cannot express the excessive 

 minuteness of the granules in question, and they estimate their 

 diameter at less than l-200^000th of an inch. Under the highest 

 powers of the microscope at present applicable such specks are hardly 

 discernible. Nevertheless, particles of this size are massive when 

 compared to physical molecules ; whence there is no reason to doubt 

 that each, small as it is, may have a molecular structure sufficiently 

 complex to give rise to the phenomena of life." Compared with such 

 embryos, cells such as those of which the substance of a leaf is com- 

 pose are giants. In a cubic inch of a leaf of the carnation there are 

 said to be upwards of three millions of cells ; in some of the cucumber 

 tribe, and in the pith of aquatic plants, what are reckoned larger cells 

 are found — they are from l-50th to l-30th of an inch in diameter ; 

 but cells are frequently seen only l-300th, l-500th, and 1-lOOOth 

 of an inch in diameter. It would be difiitiult for many to conceive of 

 the size of a cell 1-lOOOth of an inch in diameter ; but these granules, 

 were not the two hundredth part of that in diameter, and one of 

 these smallest cells, could contain sis millions of the granules in 

 question ! 



To one conversant with structures so aiinute there is nothing 



