194 



INTRODUCTION TO CRYPTOGAMIC BOTANY. 



Membranaceous or cartilaginous. Conceptacles distinct, 

 often perforated. Spores (Fig. 45, 6) formed successively, 

 beginning at the tips, in tbe joints of moniliform threads 

 which spring from a basal placenta. 



170. This section comprises those red Algoe which have their 

 spores lodged in an external subglobose conceptacle, and at 

 the same time whose spore-threads are moniliform, the joints 

 of which, commencing above, separate into many spores. Their 

 frond is either cartilaginous or membranaceous, and totally 

 different in habit from those which follow. It comprises some 

 of our most common and beautiful Algas, remarkable for their 



Fig. 48. 



a. Vertical section of conceiDtacle of Gracilaria armata, J. Ag., show- 

 ing the placenta penetrating the cavity of the nucleus, from a specimen 

 received from Lenormand, magnified. 



h. Ditto of Grinnelia Americana, Harv., showing the rudimentary 

 placenta and spore-threads. After Harvey, magnified. 



c. Ditto of Corallina officinalis, magnified. 



d. Membrane of Ditto, more highly magnified, with impressions of 

 the external cells. 



brilliant rose and purple tints. They often assume a frondose 

 aspect from the regularity of the nerves, which sometimes per- 

 form the functions of a stem, when the membranous border 

 has decayed, and give rise in turn to new fronds. As regards 

 internal structure nothing can be more various, but they never 



