PITTED TISSUE. 



17 



Fig. 50. Section of the 

 root of the ALDER TIIEE 

 (Alnus), sho-sving the 

 large-sized pores, or se- 

 mi-transparent spaces, 

 of its pitted tissue. 



It is proper to state further, that certain authorities attribute the production of cells 

 to the evolution of bubbles of gas in an azotized fluid, and they are of opinion that only by 

 that mode can we account for the extreme rapidity with which cells are developed. 



Bothrenchym, or Fitted Tissue; "We now proceed to describe the various 

 modifications of the fundamental cellular tissue, and first, that of Bothrenchym, since 

 it is very nearly allied to cellular tissue. It is so called from two Greek words signify- 

 ing pitted tissue, to indicate that a number of translucent spots are distributed over its 

 surface. We have already described the mode of formation of 

 this tissue when considering dotted cells, p. 7. It differs from 

 dotted cells chiefly in size ; for it may be regarded as a series 

 of very large cells, placed end to end, and separated from each 

 other by obliquely-placed partitions. At a later period of life 

 it puts on the character of a tube by the breaking-up and 

 removal of the partitions. Its ordinary position in plants is in 

 the stems of wooded plants, and more particularly of such as attach 

 themselves to other trees for support, and grow rapidly. Thus 

 it is met with on a thin longitudinal section of almost all trees, 

 but more readily in the alder (Fig. 50), vine, clematis, cane 

 (Rattan}^ and similar fast-growing plants, and wherever a rapid 

 circulation is proceeding. In this respect it differs from mere dotted cellular tissue, 

 since that is more commonly found in the herbaceous than wooded plants. This, in 

 common with other vegetable tissues, retains its^ characters perfectly for thousands of 

 years, as may be observed in the annexed figure of a duct (Fig. 51), 

 taken from a piece of anthracite coal. 



It is not uncommon to find a spiral fibre associated with the dotted 

 tissue, as in Fig. 52, when the tissue may be regarded as a spiral duct 

 with pores. It is a microscopic object of much interest, and very easily 

 obtained. Take a piece of common cane, and having cut away a por- 

 tion of the outside, take a thin section down the cane, and place it 

 under the microscope in a drop of water. The little 

 pits will be seen with much ease, as also the large size 

 of the tissue as compared with the woody tissue which 

 accompanies it. We have found the best illustration 

 of it in a piece of deeply-coloured rose-wood, for 

 there the dark tint of the secretion gave a peculiar 

 distinctness to the tissue. 



Its chief use in plants is to carry on the circulation with great 

 rapidity, and is therefore particularly necessary in such plants as grow 

 in southern and eastern climes, and yield refreshing juices, as, for 

 example, the vegetable fountains of India. The importance of this tissue 

 to all plants may be inferred from the large amount of vapour which 

 they throw off by perspiration. Thus an ordinary-sized cabbage, in our 

 climate, was found to perspire to the extent of 1 Ib. 9 oz., and a sun- 

 flower to that of 1 Ib. 14 oz. in a day of twelve hours ; and it is 

 evident that the great heat of southern climes must induce a far greater amount of 

 perspiration, and, by consequence, require a more active circulation. The fluid thus 

 exhaled is supplied chiefly by the bothrenchym, which therefore has a circulation 

 proceeding from the roots towards the leaves of the plant. This function is not 





Fig. 51 Porous 

 duct, from An- 

 thracite coal. 



Fig. 52. Pore?, 

 and a spiral 

 fibre, from the 

 ELM TREE ( Ul- 



mus). 



ORGANIC NATURE. No. XIII. 



