360 



BOTANY 



calcareous incrustation some forms conic to resemble coral. A'-ihil.tilnrin ni<ii;t< , - 

 ranca (**) (Fig. 294) will serve as an. example of such calcareous Algae. Tin- thin 

 stalk of the thallus is attached by means of rhizoids, while the umbrella-like disc 

 consists of closely united tubular outgrowths, each of which is to be regarded as 

 a gametangiom. The contents of the latter do not fonn the biciliate gametes 



directly, but lirst divide into a large 

 number of firm-walled cysts. The-, 

 remain in the resting condition 

 throughout the winter, and then 

 give rise to numerous gametes which 

 conjugate in pairs. The zygotes 

 germinate promptly and grow into 

 new plant-. 



Order 5. Siphonales. The Siph- 

 oneae are distinguished from the pre- 

 ceding groups of Algae by the struc- 

 ture of their thallus. which, although 

 more or less profusely branched, is 



K 11 :._". '3. Portion of Cladopho, -n ijlo,i>enit. (x48.) 

 To the ri^lit a swarm-spore, (x 1000.) 



l'i<:. 294. Acetiiliii/nriii med 

 (\at. size.) 



not at first divided by transverse septa. The cell-wall thus encloses a continuous 

 protoplasmic body in which numerous nuclei and small green chloroplasts are 

 embedded. The same type of thallus is also met with in the Phycomycetes or 

 Algal Fungi. 



The majority of the Siphoneae inhabit the sea, and on account of the com- 

 plicated segmentation of their thallus, afford one of the most interesting types 

 of algal development. The genus Caulerpa ( :M ), represented by many species 

 inhabiting the warmer water of the ocean, has a creeping main axis. Increasing 

 in length by apical growth, the stem-like portion of the thallus gives off from its 

 under surface profusely branched colourless rhizoids, while, from its upper side, 



