SECT.V. FLUID CURRENTS. 313 



like globules of a starchy nature float ; and when these 

 particles are watched with a microscope, they show that, 

 in every tube of the plant, a continual current of that 

 liquid, with its particles, ascends one of the green bands 

 and descends by the other, even when the stem and 

 branches are twisted ; but they never flow in the colour- 

 less bands, though there is nothing to hinder them. 

 According to the observations of microscopists there is 

 probably a gyration of an azotized viscid fluid in all 

 plants originating in, and maintained by, vital con- 

 tractility of structure, but in none is it so evident as 

 in the Characese. Its rate is increased by heat and 

 diminished by cold, like the circulation of the blood in 

 animals, because the activity of the vital energy bears 

 a precise relation to the quantity of heat received. 

 The gyration is instantly arrested by a shock of elec- 

 tricity. 



The reproductive organs of the Characese are of two 

 kinds, both growing in the axils of the branchlets, 

 namely, dark-red globules, which are antheridia, and 

 nucules or pistillidia, which contain germ cells. Some- 

 times they are found in different individuals, but in most 

 of the Nitellas they are in the same individual, the glo- 

 bules being placed closely below the nucules, as in fig. 41, 

 A, B. The envelope of the nearly spherical globules is 

 formed of eight spherico-triangular valves. From the 

 middle of the interior surface of these valves, a perpen- 

 dicular orange-coloured column extends to the centre 

 of the globule, where its summit is crowned with a 

 mass of confervoid filaments, which are formed of a 

 linear succession of minute cells ; while from the base 

 of the column, bands of orange-coloured spherules im- 

 bedded in gelatine radiate along the interior surface 

 of the valve to its margin as shown at c, in the same 

 figure. After successive changes in the matter within 

 the confervoid filaments, (fig. 42, D-G), the microscope 



