l68 THE ALGAE 



that have been described and a re-investigation would seem to be 

 desirable. 



REFERENCE 



Colpomenia 



Kunieda, H. and Suto, S. (1938). Bot. Mag. Tokyo, 52 , 539. 



Desmarestiales 



The plants belonging to this small order are often of large size 

 with leaf-like lateral branches. The branches terminate in branched 

 uniseriate filaments but these may also occur laterally in tufts along 

 the branches. These filaments in Desmarestia and Arthrocladia are 

 deciduous in the late growing season so that the plants have a 

 definite summer and winter aspect. There is regular alternation of 

 generations between the macroscopic diploid plant and micro- 

 scopic gametophytes. The genus Desmarestia is interesting in that 

 the cells readily Uberate small quantities of free sulphuric acid on 

 death and this causes damage to other plants that are adjacent. If 

 collected they should always be kept separate from other material. 

 The various species are restricted to the colder waters of the 

 northern and southern hemispheres. 



Desmarestiaceae : Desmarestia (after A. G. Desmarest). Fig. 95 



The plants are bushy and usually of some size (2-3 ft.), especially 

 the Pacific species. They sometimes bear gall-like sweUings which 

 are caused by a copepod. The erect, cylindrical or compressed 

 thallus arises from a disc-Hke holdfast and exhibits regular pinnate 

 branching, the branches either being elongate or else mere denticu- 

 lations. The branches bear the deciduous filaments in the denticu- 

 lations and at their apices. Morphologically the thallus is composed 

 of a single prominent central row of large cells with an intercalary 

 meristem at the base of the terminal hair. The large central cells, 

 the transverse walls of which are pitted, are surrounded by cortical 

 cells, the primary cortex being derived from the basal cells of the 

 primary laterals. These divide periclinally to give a many-layered 



