ALG/E. 1 49 1 



integument is not hardened by the deposition of lime or flint. Cer- 

 tain Tertiary fossils have been described by palseobotanists as be- 

 longing to this group of Sea-weeds, but the nature of many of these 

 is very doubtful. 



Class IV. Chlorospore^e. — This class includes a number of 

 green or olive-coloured Algae, which live in the sea or in fresh waters, 

 and which reproduce themselves by cell-division or by the develop- 

 ment of spores in special cavities, while swarm-spores occasionally 

 exist. The only group of this class which attains sufficient palseon- 

 tological importance to require special notice is that of the Siphonece 

 verticillatce. This family includes green-coloured marine Algse, in 

 which the thallus consists of a single cell, which may or may not be 

 hardened by the deposition of carbonate of lime in its wall. The 

 single cell which constitutes the entire plant may be of gigantic size, 

 comparatively speaking, and may be simple or branched. At its 

 base the cell sends out root-like prolongations, by means of which 

 it is attached to foreign bodies ; while its ascending portion gives 

 origin to whorls of lateral tubular processes. Reproduction takes 

 place by the development of swarm-spores in special cavities or 

 chambers. The few living forms of this family (Cymopolia, Neo- 

 meris, Acetabularia, &c.) are inhabitants of warm seas ; and with 

 these must be associated an extensive series of fossil types, which 

 have been commonly regarded as referable to the Fora7ni?iifera or 

 the Corals, and the real nature of which was first demonstrated by 

 Munier-Chalmas. 



As above pointed out, the thallus of the Siphonece verticillatce 

 may be simple or dichotomously branched, and consists of a single 

 axial cell, which is fixed to foreign bodies by root-like basal exten- 

 sions. The unicellular, often divided, axis gives out at intervals 

 whorls of short tubular processes (fig. 1360, b), the point of origin 

 of each whorl being commonly marked by a constriction of the stem. 

 In some cases (e.g., in Ovulites and Diplopord) the primary whorled 

 processes do not subdivide ; but in others (e.g., in Cymopolia) the 

 primary offshoots (fig. 1360, c, c) divide again into secondary pro- 

 cesses, some of which (b) are sterile, while others (a) are connected 

 with reproduction. The sterile offshoots terminate in free extremi- 

 ties which are often dilated and club-shaped, and by their apposi- 

 tion give rise to a porous superficial layer. The fertile offshoots, on 

 the other hand, constitute spherical sporangia (a), which are wider 

 than the sterile processes, and are at the same time supported upon 

 shorter stalks. 



In many forms, both the axis and the verticillate processes derived 

 from it secrete a thick calcareous crust. Where the lateral whorled 

 offshoots are simple (as in Diplopord), the calcareous crust has the 

 form of a simple thickened cylinder, traversed by transverse tubes, 



