1 72 CELLULAR TISSUE. PART n. 



increased by the successive division of the cells into four 

 equal parts, as in some of the fuci, and the solid vegetable 

 mass is formed and augmented upon the same principle, 

 so that it consists of a congeries of primordial cells or 

 globules coated with cellulose, which by mutual pressure 

 take a many-sided cellular form. Six or eight sides are 

 most common ; when six-sided, a section of the solid is 

 like honeycomb, but it frequently resembles a very ir- 

 regular fine lace or network. The form of the cells, 

 which not only depends upon the number of sides but 

 on the direction of the pressure, varies exceedingly in 

 different plants, and in different parts of the same plant. 

 The size of the cells averages from the three to the five 

 hundredth part of an inch in diameter. Some are very 

 large, as in the pulp of the orange and lemon; but in 

 the pollen of flowering plants, and other cases, they are 

 not more than the thousandth part of an inch in dia- 

 meter, consequently invisible to the naked eye. Occa- 

 sionally the cells are elongated in the direction of least 

 pressure, as in the stems and hairs of plants, or sometimes 

 they have a stellar form. In the looser and fleshy parts 

 they retain their globular form and only touch one an- 

 other, leaving triangular spaces between them filled with 

 air in water plants ; but in general the cells are held 

 together by a viscid liquid. When these intercellular 

 spaces, whether left by globular or polyangular cells, 

 are placed the one over the other for some distance, 

 they constitute intercellular passages or channels, and 

 sometimes they form lacunae or large empty spaces. 



Notwithstanding its great variety of forms, this solid 

 congeries of cells, called cellular tissue, is the universal 

 basis of vegetable structure ; it forms the principal part 

 of all plants, and the entire mass of many. Though 

 often highly coloured, as in flowers, green leaves and 

 young shoots, it is frequently hyaline and colourless. 

 The dark cells in fig. 4 represent the green part of a 



