THE ALG^ 267 



tion and further growth, to produce a new generation of 

 microspores ; i.e. pollen grains, and megaspores (embryo 

 sac), and so on, through the cycle. 



376. Relative Importance of Gametophyte and Sporophyte. 



— ■ It is important to notice that the progressive diminution 

 of the gametophyte in comparison with the sporophyte 

 which we saw taking place in proceeding from the bryo- 

 phytes to pteridophytes, reaches its climax in the spermato- 

 phytes, where it is reduced to such insignificance that it is 

 only by certain analogies of structure and function that it 

 can be recognized at all. It remains permanently inclosed 

 within the walls of the ovary and is absorbed by the sporo- 

 phyte during germination, or even earher in those seeds 

 classed as ex-albuminous. The sporophyte, on the other 

 hand, represents the fully organized plant, and attains 

 among dicotyledons the highest development of vegetable 

 structure. 



THE AJjQlE, 



Material. — Collect in a bottle some of the green scum found in 

 stagnant pools, ditches, and sluggish streams everywhere, and vari- 

 ously known as frog spit, pond scum, brook silk, etc. In cities and 

 other places where specimens are not easily procured, it can be culti- 

 vated in a simple aquarium made of a wide-mouthed glass jar with a 

 few pebbles and sticks at the bottom. 



377. Variety of Forms. — This group embraces plants 

 of the greatest diversity of form and structure, from the 

 minute volvox and desmids that hover near the uncertain 

 boundaries dividing the vegetable from the animal world, 

 to the giant kelps of the southern ocean, which sometimes 

 attain a length of from six hundred to one thousand feet. 

 The fresh-water algae are all very small, and those- of them 

 that are visible to the naked eye belong mostly to the fila- 

 mftitous group, so called from their slender threadlike thalli, 

 that look like bits of fine green floss floating about in the 

 water. 



378. Examination of a Specimen. — Place a drop or two 

 of fresh pond scum on a piece of glass and examine with 



