DEFINITION. 



69 



^vhich show a common growth, and yet consist of single elementary structures 

 developing individually (Fig. 55). 



With the exception, however, of the instances named, and of some allied 

 ones, the formation in the vegetable kingdom of many-celled bodies regulated by 

 a common growth always arises from the tissue-cells which originate by the often 

 repeated bipartition from common primary mother-cells, remaining from the very 



Fig. 56. — Epidermis (c) and subjacent cortical parenchyma 

 of the hypocotyledonary segment of the sunflower, which 

 r thickens quickly after completion of the division ; the darker, 

 thicker cell-walls are the original ones, the thinner radial 

 ones those most newly formed. The strong- tangential growth 

 even of the epidermis-cells together with their cuticle is of 

 special interest in this process. 



Fig. 55.— Part of a longitudinal section of a Gastromycete (Criicibulum vulgare), showing the course of the hyphse: their interstices 

 are filled with a watery jelly, which has probably resulted from the conversion into mucilage of the outer cell-wall layers of the 

 filaments. (For further details of the internal organisation, see Book II. Fungi. The drawing is partially diagrammatic, inasmuch as 

 the hyphse are too thick for the small magnifying of the whole (about 35), and not so numerous as in nature.) 



commencement in connexion, in consequence of the manner of formation of the 

 partition-wall; the cells are in these cases, at least originally, so united that they 

 appear at an earlier stage like chambers in a mass which continues to grow uni- 

 formly (Fig. 56). 



The two first-named kinds of tissue-formation may be distinguished as spurious from 

 the latter or genuine form ; but there is no sharp boundary-line between them. In many 

 cases, for example, the endosperm is only in its rudimentary state a spurious tissue, due 

 to the amalgamation of originally isolated cells ; in its further development by cell- 

 division it becomes a true tissue {e.g. Ricinus, &c.). The formation of tissue -surfaces 

 occurs in the formation of the cortex of many Algae and of the genus Chara, by the 

 development of single cell-filaments ; but in such a manner that by these means com- 

 binations make their appearance which can no longer be distinguished from true tissues. 



