CHAPTER VI. THE THALLOPHYTA. 3OI 



the Chlorophyceae, but some distance back of it. In many of the 

 lower forms the spores are asexual, in others some of them con- 

 jugate to produce zygospores, in still others distinct oSspheres 

 and antherozoids are produced. 



Between the last two are forms in which the sexual cells 

 differ from each other but little except in size, so that in respect 

 to reproduction, also, the group forms a closely related series. 



All the forms which produce oospheres have the peculiarity 

 that the latter are ejected from the oogonia and become entirely 

 free from the plant previous to the act of fertilization. Moreover, 

 except in a few transitorial forms, the oospheres are not endowed 

 with the power of locomotion. 



There are two principal divisions of the sub-class, the Phoeo- 

 sporece, and the Fucacece. 



The term Phaeosporeae literally means dusky-spored, and is 

 applied to the group because of the usually dark color of the 

 sporangia. Many of the species have been observed to produce 

 gemmae, or to multiply by the separation of branches ; but spore- 

 reproduction, except in Cutleria and its allies, takes place by 

 means of swarm-spores. In some species the swarm-spores have 

 been observed to conjugate, but there is no observable difference 

 between those which do and those which do not. Some species 

 produce only round, dark-colored, unilocular sporangia ; others 

 produce these and also oblong multilocular sporangia. In Cut- 

 leria two kinds of spores, one larger and the other smaller, are 

 produced in different kinds of multilocular sporangia ; the for- 

 mer are to be regarded as oospheres, the latter as antherozoids. 



The most familiar members of the group are the Laminarias 

 or Sea-aprons. These are plants of rather large size, often attain- 

 ing a length of eight or ten feet. They have cylindrical stems 

 of varying length, and often attaining the diameter of an inch 

 or more. The base is attached firmly to rocks or other marine 

 objects by means of strong, branching rhizoids, and the upper 

 part expands into a flattened, leathery, blade-like organ, which 

 in some species is entire ; in others more or less divided. The 

 blade and stem increase in length in a peculiar manner, namely, 

 by the formation of new cells at the junction of the two organs, 

 and the stem also increases in diameter by means of a growing 

 layer beneath the rind, reminding us of the grdwth of the stems 



