CELL. 



[ 119 ] 



CELL. 



Fig. 117 



grow out into arms or rays, 

 producing stellate cells, as 

 in the pith of the Rush (PI. 

 38. fig. 18), and the paren- 

 chyma of many aquatic 

 plants, in the leaf-stalk of 

 the Banana, &c. Cellswhich 

 are free, as in the lower 

 Cellular plants, sometimes 

 grow out into long tubular 

 structm-es such as Vau- 

 cheria, with a continuous cavity, and 

 indeed sometimes ramify into a complication 

 of branches, as in Bryopsis and Codium, 

 while in Botrydium (fig. 77) the globular 

 cell sends down a number of root-like fila- 

 ments which are mere protrusions of its own 

 wall. The cells of Chara attain very large 

 size. In the Flowering plants we have an 

 example of extraordinary growth of a single 

 cell in the pollen-tubes, which, in some 

 cases, become as much as three inches long. 

 Size. — The dimensions of cells vary to 

 infinity, and, indeed, often extremely in one 

 and the same tissue, but not as a rule. And 

 the diameter of cells is very frequently 

 incomparably less than the length, as in all 

 filamentous and fibrous cells. Taking a very 

 general view, we may say that parencliyma 



cells vary from 1-250" to 1 

 meter ; but the spores of 



1000' 



in dia- 

 Funffi 



, KHA.V mv/ owwiv^o wx UiaUy ^ "-'^'^ 



measure no more than 1-6000" to 1-8000", 

 while the cells of the juicy parench3ma of 

 many fruits and piths attain as much as 

 1-100". In elongated cells, such as those of 

 liber and most woods, the diameter is ordi- 

 narily less than in parenchyma, while the 

 length is far greater; thus in wood the 

 length varies from about 1-40" to 1-12", 

 while the diameters are respectively 1-300" 

 and 1-100"; in liber the length may extend 

 to 1-8" or 1-4", with a diameter of 1-800", 

 and 1-400". (See Fibres.) Hairs composed 

 of a single cell often attain a great 

 length, as in Cotton, where a single filamen- 

 tous cell may measure 1" to 2". (See Tissues, 

 Vegetable, and Primordial utricle.) 



Cells may be examined either in situ, as 

 parts of tissues, or free, sei)arated naturally 

 or artificially. For the first it is simply 

 requisite to make fine slices with a razor, in 

 various directions through the structm-e ; if 

 soft or thin it should be placed between the 

 two halves of a split vial- cork and sliced with 

 the cork, the cork being afterwards removed 

 from the object-holder with a needle. Slices 

 of many kinds of cellular tissue are made 

 more clear by the addition of a little diluted 



sulphuric acid, which, however, often swells 

 up some of the layers. 



For examining isolated or nearly separate 

 cells, we may take the lower Algae or Fungi, 

 or germinating spores of the higher plants ; 

 or we may separate the cells of the tissues of 

 higher plants. The parenchymatous tissues 

 may usually be separated into their elemen- 

 tary cells by maceration in water; the decom- 

 posing ends of tlowerstalks which have been 

 in water several days, will generally affbrd 

 tissue in such a state that it ma}' be broken 

 up with a needle. Boiling will do with some 

 of the denser kinds, while for the woody 

 tissues it is requisite to leave fragments in a 

 mixture of a small crystal of chlorate of potass 

 and a drop of nitric acid, for 12 to 24 

 hours, and wash them well with water; liber- 

 cells, woody-cellSj &c., may be isolated by 

 this means. 



Formation of Cells. — This subject has 

 undergone a great amount of investigation 

 during the last few years, and the views 

 which have been propounded at various 

 times have conflicted strongly in many points. 

 It would be exceeding our hmits, however, 

 to enter upon a critical examination of the 

 theories of cell-development, and we shall 

 therefore confine ourselves to a brief account 

 of those phasnoraena and laws of the repro- 

 duction of cells, upon v>'hich the diversity of 

 0})inion only affects suborchnate particulars. 



All vegetable cells (using this term in the 

 sense of the cellulose s(tv with contents, as 

 defined above) in which the capacit3'for repro- 

 duction exists, contain an internal structure, 

 varying in its condition and appearance at 

 diff*erent e])ochs and in different plants or 

 parts of plants, called, in accordance with 

 Mold's proposal, the jjrimordial utricle. This 

 structure consists of a collection of the ^;ro/o- 

 2)lasm, a semifluid nitrogenous substance, 

 displaying itself either as a continuous layer 

 of variable thickness, lining the cellulose 

 wall of the cell, or as amass filling the whole 

 cavity, either homogeneous or honey-combed 

 more or less by vesicular cavities filled with 

 watery cell-sap. All the other cell-contents 

 are enclosed or imbedded in this primordial 

 utricle, and with it they collectively consti- 

 tute what is called by some authors the 

 endochrome of the cell. The characters of 

 the Primordial Utricle and of the 

 Protoplasm are given in the requisite 

 detail under then* respective heads. 



In a very large number of cases, we find 

 in the primordial utricle, at this time, a pecu- 

 liar body, called the nucleus, to which some 



