* 
THE. 
AMERICAN NATURALIST. 
Vou. x1.— SEPTEMBER, is77v.— No. 9. 
REPRODUCTION IN FRESH-WATER ALG. 
BY BYRON D. HALSTED, M. 8. 
MONG the higher forms of vegetable life, two distinct 
methods of reproduction have long been observed, namely, 
by means of seeds and through some outgrowth from the parent 
plant. The first method is styled the sexual form, because there 
is involved in the production of a seed the male element, repre- 
sented by the pollen grain, and the female part called the em- 
bryonal vesicle. In fact, it is the blending of the contents of two 
Separate and distinct cells to form a germ, which under favorable 
circumstances is capable of producing a plant like the one from 
which it came. Under the second method fall all those forms of 
continuing the species other than by means of seeds, which are 
very common in nature and extensively practiced in the art of 
horticulture. In essence this is nothing more than multiplication 
by offshoots or by removal of parts of plants, which when natu- 
rally or artificially separated will continue to live and grow. 
Let us pass by the interesting and more familiar field of sex- 
ual and asexual reproduction among Phenogams, and spend a 
few moments in looking at these same methods as shown to us 
by the Algæ of our fresh-water ponds and streams. 
hen we have a plant consisting of a single cell, and in the 
Process of time the walls of that cell close in. and divide it into , 
two separate and similar cells, each of which soon attains the nor- 
mal size and divides again in the same manner, we have the 
clearest illustration of asexual reproduction. The lowest forms 
of fresh-water Algz furnish thousands of such examples, where 
the offshoot and parent plant are not distinguishable because 
equal in all respects ; and in which division of cells results in the 
multiplication of individuals in the ratio of one to two, as shown 
in Figure 85, a. In other cases the division is not so simple, for, 
“Stead of each dividing into two cells, a single unicellular in- 
Copyright, 1877, by A. S. PACKARD, JR. 
