42 THE ELEMENTARY STRUCTURE OF PLANTS. 



less ; as if the cell-membrane had extended after the thread was 

 deposited, which is probably the case. 



47. The delicate walls of some such cells are torn or obliterated 

 at maturity, while the firmer bands or fibrous markings remain in 

 the form of separate threads ; as in the tissue that lines the walls 

 of the anther (Fig. 32). In a similar manner the spirally-marked 

 tubes that are mingled with the seeds of the Hepatic Mosses are 

 converted into elastic spiral threads (Fig. 85). So, also, the del- 

 icate cells or hairs that invest the coat of some seeds, which con- 

 tain a spirally-coiled thread, give way when moistened, or are 

 torn asunder by the force with which the thread uncoils. 



48. Free Gelatinous Coils in Cells, In many cases, however, the 

 spiral deposit in the cells which form the hairs on the surface of 

 seeds, and of some seed-like fruits, remains of a gelatinous con- 

 sistence, and lies loose in the cell. When moistened, water is 

 absorbed by endosmosis, the gelatinous contents swell, burst the 

 cell-membrane (at the same time frequently forcing it away from 

 its attachment), and gush out in the form of uncoiling mucilagi- 

 nous threads. Examples of the kind are furnished by the seeds of 

 Collomia and Gilia ; and very striking ones by hairs or papillae on 

 the seed-like fruits of numerous species of Senecio and the allied 

 genera. Those of Crocidium project a thick mucilaginous twisted 

 band, in place of a thread. This structure is known to be com- 

 mon on the surface of seeds and seed-like fruits ; one purpose 

 which it subserves will be pointed out in a future chapter. 



49. Of the same nature as the last, probably, as maintained by 

 Nageli and Schleiden, are the loose bodies, thickened at one end 

 and tapering to a point at the other, which are found in the anthe- 

 ridia of Mosses and Liverworts, in the young leaves of Ferns, &c. ; 

 and which, on account of their exhibiting an active vermicular mo- 

 tion when first extricated from the cell in water, were denominat- 

 ed Phytozoa by Grisebach. 



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 which all plants are composed, irrespective of the 

 manifold forms they may assume, and of some peculiar transfor- 

 mations they may undergo. Some of these should now be speci- 



