428 INTRODUCTION TO CRYPTOGAMIC BOTANY. 



the axis, radiating in eight different directions^ and each pro- 

 ducing a whorl of branchlets, so as together to form a sphere. 

 I have seen no better or more probable explanation. Wal^ 

 roth's observation that he has seen the globules germinate, has 

 never been confirmed. 



. 471. The nucules or spores consist of a central sac filled with 

 starch cells, coated with five cells, wound spirally roimd it, the 

 tips of which are free. The nucules germinate by the forma- 

 tion of a cell at the tip of the central sac, which is soon deve- 

 loped downwards into rootlets, and upwards into a stem, so 

 that the germination looks extremely like that of a monocotyle- 

 don. There is in an early stage of growth, a canal leading down 

 to the central cell, which forms a passage for the spermatozoids. 

 Their entrance has, however, as I believe, not at present been 

 observed. 



472. One of the most remarkable phenomena about Oha- 

 racew is the circulation, which was first discovered by Corti, 

 and respecting which many _treatises have appeared. In 

 Chara, where the axillary cells are coated with an external 

 layer in the walls of which are deposited multitudes of rhom- 

 boidal crystals of carbonate of lime, it is not easy to observe 

 the phenomenon. Recourse should, therefore, be had to some 

 species of Nitella in which it may be observed distinctly with 

 any tolerable microscope. The chlorophyl grains in each arti- 

 culation are disposed in two bands in a spiral direction, so as 

 to leave a colourless quiescent space. The central fluid is inac- 

 tive, but between this and the stratum of chlorophyl a circu- 

 lation of the protoplasmic mass takes place from below, 

 upwards, till it reaches the top of the cell, when it turns down- 

 ward, ascending again when it gets to the base; and so moving 

 so long as the vital powers are active, like an endless band in 

 a piece of machinery. If a ligature * is tied round the cell, 

 the place of the hgature comports itself exactly like an ordi- 

 nary node, the downward circulation of the upper half, and 

 the upward of the lower half being diverted at that point. 



* See Dutrochet, in Ann. d. So. Nat., s6r. 2, vol. 9, tab. 2. See also 

 Donn6's Memoir, 1. c. vol 10, 346, with Dutrochet and Brongniart's 

 report. 



