76 



HUTCHINSON'S POPULAR BOTANY 



1 2 3 



FIG. 105. PORTION OF STEM OF 



ITALIAN REED. 



1. Outer covering of the stem or integument. 



2. Pibro-vascular bundle. 3. Medulla or pith, (a) 

 Tissue of cells (parenchyma); (6) Bast-fibres; 

 (c) Pitted vessel ; (/) Spiral vessels ; (g) Annular 

 vessels ; (A) Soft loose cells of pith ; (.) Sieve- 

 tubes or bast-vessels. 



new and yet finer threads presently ap- 

 pear, each of which extends from pole 

 to pole, the figure now presented to the 

 eye being that of a miniature spindle in 

 the midst of the protoplasm, and this 

 spindle becomes more and more extended 

 till it stretches across the cell. Meanwhile, 

 along the fibres stream granules of proto- 

 plasm, which, gathering where the spindle 

 is widest (i.e. exactly > midway between 

 the poles), unite to form a plate ; while 

 the specks of congested protoplasm which 

 constitute the ends of the spindle become 

 distinct and perfect nuclei. From the 

 plate thus formed is developed in time a 

 wall of cellulose, by which the entire 

 cavity of the mother-cell is divided into 

 two chambers ; and then, with the dis- 

 appearance of thefibrillce, the nuclei finally 

 part company, and cell division is accom- 

 plished. 

 Such, then, are the principal means of cell 



multiplication free-cell formation, rejuven- 

 escence, conjugation, and cell division; and this 



leads us to another important subject that of 



cell fusion with which we may link what little 



there is to say about vegetable tissues, and then 



close this division of our subject. 



Any set of similar cells, governed by a com- 

 mon law of growth, forms a tissue, and two or 



more cells, coalescing into a single individual 



by the partial or entire breaking down of their 



dividing walls, form a vessel. The latter process 



is cell fusion. We have seen an example of 



tissue already in the stellate cells of the Bean 



(fig. 44) ; the fragment of Onion-skin shown in 



fig. 35 was another example. The diagram now 



given (fig. 105) offers examples both of vessels 



and tissues, c, /, and g are vessels, a and h are 



tissues of cells. The darkly shaded portion at b is 



woody fibre, of which we shall speak again in a 



moment. The subject need present no difficul- 

 ties, as the ground has been already cleared by 



the remarks upon cell forms and structure ; but 



FIG. 106. LONGITUDINAL 



SECTION OF A PORTION OF 



THE CORTICAL PARENCHYMA 



OF A EUPHORBIA, 



Showing laticiferous or branched 



laticiferous "cell" (7) in the midst 



of the tissue. 



