662 



SCIENTIFIC RECREATIONS. 



Fig- 739. Plant cells. 



kind of jelly-like substance (which holds the proteine or basis of life) ; 

 (2) water or cell-sap ; (3) the nucleus ; and (4) chlorophyl. This 



protoplasm is apparent in both 

 plants and animals. The cells con- 

 taining these various substances 

 in which we find oxygen, hydrogen, 

 nitrogen, sulphur, and carbon, with 

 phosphorus perhaps are divided 

 to form new cells, and so on with 

 most astonishing rapidity, amounting 

 in some instances to millions in a 

 day, and a case of this nature will readily be recognized in the mushroom. 



Cellular tissue is composed of these cells, and vascular tissue is composed of 

 vessels or tubes like coiled springs, which are cells without divisions or parti- 

 tions. These tissues will be referred to farther on as dotted ducts or tubes. 



In most of the spongy parts of plants, as in the pulp of fruits and pith of 

 elder, the cells preserve the globular or oval shape represented in fig. 739 A. 

 But the cells, in consequence of that mutual pressure, more frequently assume 

 the form of a polygon (fig 739 B), the section of which is generally hexagonal. 

 The cellular tissue may generally be compared to the bubbles produced by 

 blowing through a straw or tobacco-pipe into soap and water; or it may be 

 illustrated by placing balls of moist clay together, and then pressing them 

 more or less strongly. In this manner every individual ball 

 assumes a polygonal shape corresponding to the form of the cells 

 represented in fig. 739 C, and which disposition is, in many plants, 

 preserved with the utmost regularity. Such cells as are, with 

 tolerable equality, extended in all directions, are named parenchyma, 

 and of these are composed the tuberous parts of plants, as the 

 potato, dahlia-roots, etc., and especially the soft, spongy parts of 

 the pith, bark, leaves, etc. We frequently, however, meet with cells 

 which are extended longitudinally, and pointed at both extre- 

 mities, as in fig. 740. The sections of these cells, which are com- 

 pactly arranged, have the appearance of a hexagon. They are 

 termed woody cells, or woody tissue (prosenchyma), and con- 

 stitute the chief portions of the more solid parts of plants, as 

 the ligneous parts of trees, shrubs, etc. Very long, flexible cells, 

 as those which constitute the fibres of flax and hemp, are called 

 bast-cells, and appear under the miscroscope as round threads of 

 uniform thickness, whereas the fibres of cotton wool, which 

 rarely exceed one or two inches in length, when magnified, present Formofcells - 

 the appearance of flattish bands with somewhat rounded margins. By these 

 marks, the union of flax and cotton in the same web or piece of cloth may 

 be detected. 



Occasionally the cells assume very abnormal shapes, as the stellate or 

 star-formed Cells, These are described as irregular cells. 



Fig. 740 



