FRESH-WATER ALGJE OF THE UNITED STATES. 193 



undergoes absorption, so that the cavities of the two cells are more or less com- 

 pletely thrown into one. All or nearly all of the contents of the proximal cell 

 now slowly pass into the distal one, which thus becomes crowded with chloro- 

 phyllous protoplasm. At or before this period, the distal receiving cell undergoes 

 a change in form, widening out greatly, and sometimes appearing actually to 

 shorten, so that it is in most instances resolved into a more or less regular globose 

 or oval cell. As the sporangium or spore-case thus formed perfects itself the endo- 

 chromes of the two cells become completely fused into one mass, which gradually 

 condenses and assumes a regular shape, until, in the form of the perfected female 

 or receptive germ, it is a dark, opaque ball more or less completely filling the spo- 

 rangial cell. At the same time, in order to afford passage for the male germ, an 

 opening is formed through the walls of the sporangium. This happens in two ways. 

 The simplest of these is by the formation of one or more circular openings or 

 pores in the wall. This pore is sometimes below, sometimes above the equatorial line. 

 Its position, numbers, and form afford good specific characters. The second method 

 is by the development of a little trap-door entrance at the distal end of the spore- 

 case. This method is unknown in our American flora, and, never having seen it, 

 I must refer to the papers of Pringsheim for details. 



The above-described mode of origin of the sporangium is the common one. In 

 0. mirabile. Wood, however, but one cell is concerned. This cell grows to an 

 enormous size, far beyond that of its fellows, and its endochrome collects into the 

 upper half of it, to be at last shut off from the lower half of the cell by the forma- 

 tion of a new cellulose partition or end wall ; or, in other words, the parent cell 

 divides by a modified process of cell division, different from that common in the 

 family. The distal daughter-cell contains all the endochrome. After the changes 

 are completed, the appearance is the same as ordinarily presented, namely, an empty 

 cell surmounted by the sporangium. Sometimes, even in plants in which the ordi- 

 nary process occurs elsewhere, a single cell appears at times to have sufficient 

 vitality to develop into a sporangium without aid from its neighbor, so that the 

 latter will preserve its integrity, and the resting spore finally lie in proximity to a 

 cell full of endochrome. 



In the moneecious (Edogoniacece, a single filament produces both the male and 

 female germs. Certain cells appear to be set apart to develop into sporangia, whilst 

 others give origin to the spermatozoids. No such plants have as yet been detected 

 in North America, and I, therefore, pass on without speaking more in detaU. - 



The second method in which the spermatozoids are produced is the most com- 

 mon in our flora ; it is the so-called gynandrous plan. In this the single filament 

 produces the female germs directly and the male germs indirectly. The former 

 arise in the way previously described, whilst the latter are the resultant of a 

 complex series of life actions, as follows : One of the main cells of the originating 

 filament, differing in no perceptible way from its fellows, instead of like them 

 developing new cells, divides up by a simple process of cell division into two or 

 more cells, each one of which contains very largely of chlorophyllous protoplasm. The 

 protoplasm within each of these secondary or daughter-cells soon condenses into an 

 irregularly ovate or conical mass, which often, even within the cell, may be seen to 



25 September, 1S72. 



