Grhinellia americana, Harv. \ \ 



formation of three to six transverse walls, lateral branches 

 develop, forming the holdfasts of the young plant (Fig. 7 h). 

 These are usually only a few cells in length, irregular in outline 

 and incurved at the tip, enabling them to fix the young 

 plant firmly to its substratum. Because of the nature of its 

 holdfasts, the young fronds are often found growing in 

 epiphytic fashion on older Grinnellia-i)\3jnts and other Algae. 



At this period, the rapid growth in the middle of the 

 filament is characterized by the appearance of vacuoles and 

 the rearrangement of chromatophores in such definitely 

 transverse and radiating lines that the appearance of cell- 

 division is produced. As the spore continues developing, 

 these lines of chromatophores are arranged lengthwise of the 

 cells (Fig. 7 c), vacuoles appear and the colour of the contents 

 becomes much lighter and almost disappears in the outer 

 terminal cells of the filament (Fig. 7 v). 



Cell-division in the germinating spore is limited to one 

 plane until the formation of a frond proper begins, when 

 fission takes place in two planes along the lines of the collected 

 chromatophores ; and subsequently, with the development of 

 the midrib, occurs in three planes in the median region of 

 the frond. 



For frequent observation of the progress of germination, 

 pieces of mica were placed beneath the fronds until sufficiently 

 covered with spores. The mica was then transferred to 

 shallow dishes of water, and was examined often during the 

 early stages of spore development. This recurring disturbance 

 proved injurious to the spores, and they seldom survived the 

 treatment longer than a week. When unmolested and 

 supplied with fresh water daily, they continued to grow for 

 a period of two to three weeks. 



To determine the varying effect of different rays of light 

 upon their development, dishes containing spores were 

 covered with colourless, red and blue glass respectively. These 

 receptacles were then protected from direct sunlight, and 

 supplied with the boiled sea-water which was changed every 

 thirty-six to forty-eight hours. The spores under the colour- 



