166 THALLOPHYTA. [CH- 



in fig. 34. The thallus consists of a delicate stalk attached to the 

 substratum by a tuft of basal holdfasts, and expanded distally into 

 a small circular disc 10 — 12 mm. in diameter and more or less 

 concave above. This terminal cap is made up of a number of 

 laterally fused appendages given off from the upper part of the 

 stalk in the form of a crowded whorl. The whole thallus resem- 

 bles a small and long-stalked calcareous fungus. In each radially 

 elongated compartment of the fertile cap (fig. 33, 1) there are 

 several sporangia (gametangia) developed; these eventually 

 open and produce numerous ciliated gametes which give rise to 

 zygospores by conjugation. Fig. 33, 1, represents the cap of an 

 Acetabularia in radial section and surface-view ; the two radial 

 compartments seen in section contain the elliptical gametangia ; 

 the circular markings at the base of the figure are scars of 

 sterile deciduous branches. 



The whole plant is unicellular, each chamber in the disc 

 being in open communication with the stem of the plant. 



Acicularia. Fig. 33, C — H. 



In a recent monograph on the Acetabularieae, Solms-Laubach' 

 lias described a new type of these algae which is of special 

 importance from the point of view of the past history of the 

 family. Mobius described an example of Acetabularia in 1889 

 under the name A. Scheiicki; this species has since been 

 placed in D'Archiac's genus Acicularia^ Acicularia Schencki' 

 bears a close resemblance as regards external form to Aceta- 

 bularia mediterranea. In the latter species the walls of the 

 terminal disc compartments are calcified, and the cavity of each 

 of the laterally fused members contains numerous free spores; 

 in Acicularia, the cavity of each disc-ray is occupied by a cal- 

 careous substance in the form of a spicule containing numerous 

 cavities in each of which is a single sporangium. A single 

 spicule is seen in fig. 33, H, showing the spherical pockets in 

 which the sporangia were originally situated. This species, 



1 Solms-Laubaoh (95»). = D'Arehiac (43) p. 386, PI. xxv. fig. 8. 



3 Solms-Laubach loc. cit. p. 38, PI. iii. 



