40 THE ELEMENTARY STRUCTURE OF PLANTS. 



occurs in the tissue that hnes the walls of the anther; and in this 

 way tlie spirally marked tubes (called Elaters) which occur in the 

 spore-cases of the Hepatic Mosses or Liverworts are converted into 

 elastic spiral threads. Of a similar nature are the 



49. Gelatinous Coils, or soft spiral threads, such as occur in the 

 hairs or projecting cells which invest the coats of many seeds or 

 seed-like fruits, and which when moistened often uncoil and are 

 projected from the bursting cell in a striking manner. When water 

 is applied, this is absorbed by endosmosis (40), the gelatinous threads 

 swell, burst the cell-membrane, and gush out in the form of uncoil- 

 ing mucilaginous fibres or bands. Good examples of the kind are 

 furnished by the seeds of CoUomia and Gilia, and by hairs or papillte 

 on the seed-like fruits of numerous sjiecies of Senecio and the allied 

 genera. Those of Crocidium project a thick, mucilaginous, twisted 

 band, in place of a thread. They may subserve a useful purpose in 

 fixing light seeds to the ground where they lodge, by means of the 

 moisture of the first shower they receive. 



Sect. III. Of the Kinds or Transformations of Cellular 

 Tissue; viz. Woody Tissue, Ducts, etc. 



50. The statements of the preceding section apply in general to 

 the cells of Avhich all plants are composed, irrespective of the mani- 

 fold forms they may assume, and of some pecuUar transformations 

 they may undergo. Some of these should now be specified ; as 

 they give rise to kinds of tissue so unlike the ordinary cellular, in 

 outward appearance at least, that they have always been distin- 

 guished by special names. We allude particularly to Woody Tissue 

 or Woody Fibre, and Vascular Tissue or Vessels, of various foi'ms. 

 These, although formerly regarded as of independent origin, are 

 now known to be mere modifications of one common type, the cell, 

 and are produced m the same mode as ordinary cells. So all the 

 statements of the foregoing section, in respect to the formation, mul- 

 tiplication, and growth of cells, are equally applicable to these also. 

 Some kinds differ from ordinary cells in shape alone ; others result 

 from their combination or confluence. This is shown in two ways : 

 first, by noting the intermediate gradations which may be found be- 

 tween every particular sort ; and secondly, by watching their de- 

 velopment and tracing them directly from tlieii' eai'liest condition, as 



