44 MORPHOLOGY 



grains and oil drops. The complexity arises from the fact that the 

 oogonium is closely invested by spirally wound elongated cells that 

 arise from the cell beneath. Above the oogonium each investing cell 

 cuts off a tip cell, the cluster of tip cells forming the so-called crown 

 (figs. 115, 116). In fertilization the crown cells spread apart at the 

 base, leaving five small slits, through which the sperms pass. Upon the 

 formation of the oospore, the walls of the envelope cells thicken and 

 harden, forming a nutlike spore case, which is the resting stage. Upon 

 germination, the oospore sends out a simple filament and an elongated 

 rhizoidal cell, a structure called the proembryo, and from the proembryo 

 the adult shoot arises as a lateral branch. The adult plants, therefore, 

 arise as lateral branches from a very different body. 



Conclusions. It is evident that the Charales cannot be related to 

 the other green algae, since they differ strikingly in vegetative body, 

 sex organs, sperms, and life history in all of which particulars the 

 resemblances are rather with the higher plants. They should at least 

 be isolated as a distinct group of Thallophytes, or preferably should 

 constitute a group between Thallophytes and Bryophytes. 



(2) PHAEOPHYCEAE 



General character. The brown algae are almost all marine. They 

 occur on all seacoasts, but are more abundant and conspicuous in the 

 cooler waters. The forms exposed to tidal action have tough, leathery, 

 and firmly anchored bodies, which sometimes reach such dimensions as 

 hundreds of feet in length. They are also often highly differentiated, 

 both as to form and tissues. The nature of the characteristic pigment 

 or pigments is in doubt. The green constituent may or may not be 

 chlorophyll, but in any event there are also present certain brown or 

 yellow constituents which give the characteristic color to the plants, 

 referred to in the name of the group. It must not be supposed that all 

 brown algae are necessarily brown, for there are gradations in the hue 

 of the bodies from brown to olive green, but the characteristic brown or 

 yellow constituents are always present. Two of these constituents have 

 been separated and named phycoxanihin and phycophaein. Another 

 general character of brown algae is that all the motile cells (zoospores 

 and sperms) are laterally biciliate, in sharp contrast with the apically 

 ciliate cells of most algae. 



The group is regarded as a highly specialized one, giving little or no 

 indication of its origin. There is certainly no indication that it has 



