te 250 a SH truckail ee Physiologica Botany. Bes ne 
granules in the living cells, sometimes broad biadd often. 
curved spirally, as in Sperogyra (Fig. 41, p. 25), sometimes 
elegant discs, the forms of which are characteristic of par- 
ticular genera. It is also not uncommon for the chlorophyll- 
grains to be imbedded in coloured fluids. On the death | Sa 
of the plant these colouring matters commonly undergo a 
change, so that, when dried, Algze seldom retain the beauti- 
-ful colours of the living plant. | 
The reproduction of Algze is effected in a number of 
different ways ; viz. :— 
1. By /ésszon or Division ; the plant dividing into two 
new individuals. This occurs especially in the Diatomacez. 
| 2. By Gemme, which become detached from the parent- 
plant as single cells, rarely as masses of cells, and grow into 
new independent plants. Of this nature are the ¢efraspores 
of the Florideae (Fig. 382) ; and a similar mode occurs also 
in Spirogyra, Zygnema, Ulothrix, &c. 
3. By Swarmspores or Zoospores (Fig. 82, p. 56, and Fig. 
385). One or more naked primordial cells are formed ~ 
free-cell formation in a particular cell of the parent-plant, 
become free by rupturing its cell-wall, and then swim about 
in the water for a longer or shorter time, like infusoria, by - 
means of two, four, or a larger number of vibratile cilia with 
which they are provided. ‘They are microscopic and desti- 
tute of a cell-wall ; but, after gradually coming to rest, de- ~ 
velope a cell-wall of cellulose, and then grow into a new . 
Alga. They occur in both freshwater and marine Alge, 
Vaucherta, Gdogonium, &c. 
4. By the formation of Oospores or Embryos from the 
coalescence of the contents. of two cells. The simplest 
variety of this process is that known as Conjugation, in 
which no difference is perceptible between the fertilisng 
and the fertilised cells (Fig. 54, p. 32, and Fig. 383). This 
occurs in the Conjugate and Diatomacez. Less frequently 
two swarmspores, one of which exceeds the other in size 
many times, coalesce, the product of their union being 2 a. 
