CELLULAR TISSUES. 



229 



Fig. 132. Stellate tissue, from stein 

 of a Rush. 



Fig. 132, in the stellate tissue cut from the stem of a 



j we have the forma- 

 tive network dividing into 

 ducts for the purpose of 

 conveying the juices to 

 the leaves of the plant. 

 These ducts may undergo 

 other transformations; the 

 cell itself become gra- 

 dually changed into a 

 spiral continuous tube or 

 duct, as seen in fig. 155; 

 these are sometimes formed by the breaking down of the 

 partitions; in the centre of which we may have a com- 

 pound spiral duct, resembling portions of tracheae from 

 the silkworm. 



Another important change occurs in the original cell, 

 it is that of its conversion into woody fibre. Common 

 woody fibre (Pleurenchyma) 

 has its sides free from de- 

 finite markings. In the 

 coniferous plants, the tubes 

 are furnished with circular 

 discs ; these discs are 

 thought to be contrivances 

 to enable the tubules of 



the WOOdy tissues tO dis- Fig. 133.^ section of stem of Clematis, 

 r i v / VJith pores, hiqhly magnified, to show 



charge their contents from the line which passes rolnd them. 

 one to the other, or into the 



cellular spaces. Such plants as have aromatic secretions are 

 furnished with glands, a circumstance which has led to 

 the division of woody tissue into simple and glandular. 

 A large central gland is seen in a section of a leaf from 

 Ficus elastica, India-rubber-tree, fig. 134, No. 2. Professor 

 Quekett observes, " The nature of the pores, or discs, in 

 conifers, has long been a subject for controversy; it is now 

 certain that the bordered pores are not peculiar to one 

 fibre, but are formed between two 'contiguous to each 

 other, and always exist in greatest numbers on those sides 

 of the woody fibres parallel to the medullary rays. They 

 are hollow; their shape biconvex; and in their centre is 



