32 BOTANY. 



the temperature out of doors approaches the freezing point. Then it is 

 only necessary to keep the plants in a warm room until about 10 P.M., when 

 they may be put out of doors for the night. On bringing them in in the 

 morning, the division will begin almost at once, and may be easily 

 studied. The nucleus divides into two parts, which remain for a time 

 connected by delicate threads (Fig. 18, J5), that finally disappear. At 

 first no nucleoli are present in the daughter nuclei, but they appear before 

 the division is complete. 



New filaments are formed by the breaking up of the old ones, this 

 sometimes being very rapid. As the cells break apart, the free ends bulge 

 strongly, showing the pressure exerted upon the cell wall by the contents 

 (Fig. 18, A). 



Spores like those of (Edogonium are formed, but the process 

 is somewhat different. It occurs in most species late in the 

 spring, but may sometimes be met with at other times. The 

 masses of fruiting plants usually appear brownish colored. If 

 spores have been formed they can, in the larger species at 

 least, *be seen with a hand lens, appearing as rows of dark- 

 colored specks. 



Two filaments lying side by side send out protuberances of the cell 

 wall that grow toward each other until they touch (Fig. 18, D). At the 

 point of contact, the wall is absorbed, forming a continuous channel 

 from one cell to the other. This process usually takes place in all the 

 cells of the two filaments, so that the two filaments, connected by tubes at 

 regular intervals, have the form of a ladder. 



In some species adjoining cells of the same filament become connected, 

 the tubes being formed at the end of the cells (Fig. 18, #), and the cell in 

 which the spore is formed enlarges. 



Soon after the channel is completed, the contents of one cell flow slowly 

 through it into the neighboring cell, and the protoplasm of the two fuses 

 into one mass. (The union of the nuclei has also been observed.) The 

 young spore thus formed contracts somewhat, becoming oval in form, and 

 soon secretes a thick wall, colorless at first, but afterwards becoming 

 brown and more or less opaque. The chlorophyll bands, although much 

 crowded, are at first distinguishable, but later lose the chlorophyll, and 

 become unrecognizable. Like the resting spores of (Edogonium these 

 require a long period of rest before germinating. 



There are various genera of the pond scums, differing in the 

 form of the chloroplasts and also in the position of the spores. 



