and Laboratory Methods. 2473 



in a delicate sac and divides into a four-celled body (the sporophyte) which gives 

 rise to four nonsexual zoospores. If material is at hand, study and draw. 



8. Write out a careful description of the entire life history of this plant, 

 noting especially that it has an alternation of generations. 



XLIII. Coleocluete puh'inata A. Br. Family, Coleochaitaceae. 



Several species of Coleochaete are to be found growing attached to the sur- 

 face of various submerged, fresh water plants. The species mentioned above 

 forms hemispherical masses of closely packed, branched filaments. These 

 masses are large enough to be seen with the naked eye and should be looked 

 for on the petioles or lamina of water lilies and other hydrophytes. 



1. Pick off some of the smaller and larger masses with a scalpel, mount, 

 and examine under low power. Under high power draw a part of the branching 

 filaments, showing the joint-like cells, each with a nucleus, chloroplast, and pyre- 

 noid, and some with long, narrow, hair-like projections sheathed at the base. 



2. Look for nonsexual reproduction by means of zoospores, a single one 

 being produced in a cell. If these are present draw and find how they escape 

 from the cell. 



3. Draw the mature oogonium, showing the oosphere and long slender, open 

 neck. How different from Batrachospermum ? 



4. Draw one of the antheridia, which are terminal or lateral flask-shaped 

 cells of peculiar form easily distinguished from the vegetative cells. Each 

 antheridium produces a single, biflagellate spermatozoid. Compare with Batrach- 

 ospermum. 



5. Draw a mature spermatozoid either free or in the antheridium. 



6. Draw an oogonium in which the egg has been fertilized, and around which 

 branches are developing from the base. 



7. Draw an oogonium containing a ripe oospore and a cortical layer of 

 close-fitting branches. 



8. From material gathered in early spring or from prepared slides, study 

 fruiting bodies in which a small sporophyte has developed by the division of the 

 oospore into a number of cells. Note the advance of the sporophyte over that 

 of Oedogonium. How many cells does it contain ? 



9. Each cell of the small, oval sporophyte develops a zoospore, which after 

 a period of activity settles down and develops into a new Coleochaete thallus. It 

 is evident from the above that the entire sporophyte of Coleochaete is sporo- 

 genous. 



10. Make a diagram in the notes, showing the life cycle of Coleochaete. 

 See Fig. 6. 



11. If material is at hand study the flat, disc-like thallus of Coleochcete scutata 

 Breb. Draw under high power and describe. 



12. Note. The Coleochaete are the algae which come nearest to the next 

 higher sub-kingdom, and, on account of the similarity of the body and the life 

 cycle, the ancestors of the lowest liverworts of the present time are supposed to 

 have been plants which in general characters were very much like them. 



