

CIRCULATION IN CKLLS. 31 



indefinitely from one end, by a sort of gemmation or budding growth, 

 •while all the rest remains stationary, or while the opposite extremity 

 is dead or decaying. Fig. 20 would represent a case of the kind, 

 except that partitions form, as the upper end grows on, dividing the 

 tube into a toav of cylindrical cells. Sometimes a new point of 

 growth commences on the side of a cell, so giving rise to 



38. Branching Cells. The hair- 

 like bodies that copiously appear 

 on the surface of young rootlets 

 furnish examples of the kind, as 

 is shown in Fig. 1, 23, 24. More 

 conspicuous examples are furnish- 

 ed by certain Algae of the simplest 

 structure, where the cell branches 

 profusely as it elongates, but the 

 tubes are all perfectly continu- 

 ous throughout ; as in Botrydium 

 (Fig. 88), where an originally 

 spherical cell is extended and 

 ramified below in the fashion of 

 a root; in Vaucheria (Fig. 89), 



where a slender tube forks or branches sparingly ; and in Bryopsis 

 (Fig. 91), where numerous branches are symmetrically arranged in 

 two opposite rows, like the plume of a feather. In these cases, the 

 fully developed plant, with all its 

 branches, is only one proliferous 

 cell, extended from various points 

 by this faculty of continuous bud- 

 ding growth. The mycelium or 

 spawn of Mushrooms, and the in- 

 tricate threads of Moulds (Fig. 

 92-94) are formed of very attenuated branching cells. And in 

 Lichens and many Fungi, cells of this kind are densely interwoven 

 into a filamentous tissue (Fig. 25). 



39. Cyclosis or Circulation in Cells. In all young cells, probably, 



at least at some period, the fluid protoplasm interposed between the 

 cell-walls and the watery sap is in a state of movement. Under 



FIG 23 Magnified cellular tissue from the rootlet of a seedling Maple ; some of the ex- 

 ternal cells growing out into root-hairs 24 A few of fie cells more highly magnified 



FIG 25 Entangled, filamentous, branching cells from the fibrous tissue of the Reindeer 

 Lichen (Cladonia rangiferina), magnified. 



