GENERAL DIFFERENTIATION OF THE PLANT-BODY 



cell behaves therefore differently from the other cells of the colony, but at the 



same time each one of ihese is able to take over the work of producing adhesive 



mucilage. 



In Licmophora flabellata, Ag. (L. radians, Kiitz.), which is represented in Fig. 5, 



a different construction of the single members of the colonies is only apparent. 



The cells here sit in a fan-like arrangement upon the somewhat broadened end 



of a branched gelatinous stalk, the branches of which 

 differ in strength. Some are short and thin and carry 

 only few cells, others again are much thicker and 

 longer and bear many cells. This appearance is 

 explained by the fact that the gelatinous substance 

 is excreted at the under end of the cells and that single 

 cells may separate themselves from the others ; as they 

 separate they build with their gelatinous excretion 

 a new stalk which must be necessarily thinner and 

 shorter than that which belongs to a larger number 

 of cells. A structure is produced in this way which 

 may be very like a monopodial system of branching, 

 but the similarity is only superficial, for the cells are 

 all equal and the separation of single ones is not a 

 regular process. The case would be very different 

 if the cells of the 'side-branches' were after some 

 time to lose their capacity for growth and division, 

 whilst those at the top of the chief axes retained 

 these powers. There is however neither an external 

 nor an internal ground for assuming this in these 

 cells which are bound together only by a gelatinous 

 envelope l . 



The algal genus Hydrurus supplies an illustration 

 of special prominence. The plants in this genus consist 

 of richly-branched gelatinous threads, sometimes many 

 metres long, which are frequently found in freshwater 

 streams and rivers. There is really here a greatly 

 developed colony of brown Flagellatae, and one can 

 easily recognize that every cell has five or six pulsating 



FIG. 5. Licirophora flabellata. . r1 ,i i_- u *u l 



Diatom-colony with branched geia- vacuoles like those which occur otherwise only in 



swarm-cells. The single energids are embedded in 



a gelatinous substance, and even in the germination of the propagative cells the 

 secretion of the slime is considerable upon that portion of them which is turned 

 towards the substratum where it forms a fixing organ (Fig. 6, /). The energids 



1 Similar branching is observed in Nevskia ramosa, a remarkable Schizomycete ; see Famintzin 

 in Bull, de 1'Acad. de Sc. de St.-Petersbourg, nouv. ser. ii (xxxiv), 1892, p. 481. For an account 

 of the interesting formation of colonies in Myxobacteria see Thaxter, in Botanical Gazette, 1892 ; 

 a division of labour appears in the plants so that all the cells of the colony are not equal 

 in capacity of development. 



