Some of the species of coleochæte consist of branched threads, while others form circular cushions several layers in thickness. These forms together with the form of our plant C. scutata make an interesting series of transitional forms from filamentous structures to an expanded plant body formed of a mass of cells.
330. COMPARATIVE TABLE FOR SPIROGYRA, VAUCHERIA, ŒDOGONIUM, COLEOCHÆTE.
| GAMETOPHYTE. (Bears the sexual organs and gonidia.) | SPOROPHYTE Bears spores | How Veg. Phase of Gametophyte is Developed. | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Vegetative Phase | Growth. | Mulitipl- ication. | Sexual Reproduction. | ||||||
| Sexual Organs. | Gametes. | Fruit. | |||||||
| Spirogyra. | Simple threads of cylindrical cells. | All cells divide and grow. | By breaking up of threads. | Undifferentiated. | Undifferentiated. | Zygospore | Develops vegetative phase directly. | ||
Any cell of thread. Conjugate by tube. | Entire contents of cojugating cells. | ||||||||
| Vaucheria. | Branched threads, continuous. | Limited to ends of threads and branches. | By multiciliate zoogonidia, and other cells, from terminal portions. | Differentiated. | Differentiated. | Egg (or oospore). Rests. | Develops vegetative phase directly. | ||
Antheridia slender cells on special branches. | Oogonium, large rounded cell on special branch, opens and emits bit of protoplasm. | Small two-ciliated spermatozoids. | Large egg cell. | ||||||
| Œdogonium. | Simple threads of cylindrical cells. | Limited to certain portions of thread. | By oval zoogonidia, with crown of cilia. Any cell may form a single zoogonidium. | Differentiated. | Differentiated. | Egg (or oospore). Rests. | Divides into four cells; each forms zoospore which develops veg.phase again. | ||
Antheridia disk-shaped, several from one vegetative cell. Sometimes on dwarf males. | Oogonium, changed vegetative cell, opens and emits bit of protoplasm. | Oval spermatozoids with crown of cilia. Two from each antheridium. | Large egg cell. | ||||||
| Coleochæte. | Branched threads, or compact circular plates. | Terminal or marginal. | By zoogonidia with two cilia. Any cell may form a single zoogonidium. | Differentiated. | Differentiated. | Egg (surrounded by wall from gametophyte). Rests. Divides and grows to form a mass of cells. | Each forms a zoospore. Zoospore develops veg. phase again. | ||
Antheridia, four or several from single veg. cell. | Oogonium, enlarged veg. cell, with long tube through opening of which spermatozoid enters. After fertilization wall of enveloping threads surrounds oogonium. | Oval, biciliate spermatozoid, one from each ntheridium. | Large egg cell. | ||||||
[CHAPTER XVIII.]
CLASSIFICATION AND ADDITIONAL
STUDIES OF THE ALGÆ.
In order to show the general relationship of the algæ studied, the principal classes are here enumerated as well as some of the families. In some of the groups not represented by the examples studied above, a few species are described which may serve as the basis of additional studies if desired. The principal classes[17] of algæ are as follows:
Class Chlorophyceæ.
331. These are the green algæ, so called because the chlorophyll green is usually not masked by other pigments, though in some forms it is. There are three subclasses.
332. Subclass PROTOCOCCOIDEÆ.—In the Protococcoideæ are found the simplest green plants. Many of them consist of single cells which live an independent life. Others form “colonies,” loose aggregations of individuals not yet having attained the permanency of even a simple plant body, for the cells often separate readily and are able to form new colonies. The colonies are often held together by a gelatinous membrane, or matrix. Some are motile, while others are non-motile. A few of the families are here enumerated.