144 



INTRODUCTION TO CETPTOGAMIC BOTANY. 



I have a beautiful species which has its seat on old bones in 

 South Carolina. The most singular habit is, however, pos- 

 sessed by one genus, analogous to that of the larger floating 

 Algae. But instead of forming circumscribed patches, it 

 spreads for many miles over the surface of the sea, according 

 to the direction of the wind, in the form of a red brown scum, 

 the little faggots of threads of which it is composed, resem- 



Fig. 36. 



Tridiodesmium erythraium, Ehr. 



Magnified from specimens collected by Mr. Darwin, compared with 

 Dr. Montague's analysis in Ann. d. Sc. Nat., Ser. 3, vol. ii. tab. 10. 



bling minute fragments of chopped hay. It is even conjectured 

 that the Red Sea may have acquired its denomination from 

 this little Alga, which is very prevalent there, and forms a 

 conspicuous object to all observing navigators.* It is curious 

 that, in some instances, this scum emits a disagreeable pungent 

 smell, affecting strongly the mucous membrane, and thereby 

 causing temporary inflammation of the eyes and troublesome 

 sneezing. The property of emitting an unpleasant odour is 



* One of the earliest notices of this phenomenon is in Osbeck's 

 Voyage. 



