38 GENERAL DIFFERENTIATION OF THE PLANT-BODY 



2. Short shoots. These are placed in a whorl and arise from the oldest 

 cortical cells of the stem. Pringsheim called them ' leaves,' and from the outset 

 they are laid down differently from the long shoots. See Fig. 13. 



3. ' Fructification leaves/ These are short shoots which bear the propagative 

 organs. They are generally like the ' leaves ' but are distinguished from them by 

 a simpler anatomical construction and by their position, for they are formed 

 specially at the end of the period of vegetation in a regular way on the older 

 segments of the stem. 



4. ' Hairs.' These are rows of cells which are formed on the 'leaves.' 



5. Adventitious shoots. These proceed from the central cells of the axis *. 

 The point that first strikes one here is that the different members are different 



in their origin, and this is not the case in Halopteris. 



An analogous differentiation of long shoots and short shoots is found also in 

 many Florideae. and some examples of this which will illustrate well the division 

 of labour among short shoots may be here briefly cited. I select for the purpose 

 some freshwater-forms which are found at the mouths of rivers in Guiana attached 

 to the mangroves and other swamp-plants 2 . 



Bostrychia Moritziana is a floridean alga with a feathered branch-system. 

 The axes which are constructed to support the branch-system are cell-masses of 

 a more complex structure than the ends of the branches, which are merely cell- 

 rows. The chief axis however ends in a cell-row. The feathered branches have 

 a limited growth and they appear as short twigs of different orders which are 

 arrested at an earlier or later stage of development. The branching at the apex 

 appears to be forked, but it is really monopodial. The lateral twig arises in 

 the apical cell by the separation through a long dividing wall of a segment which 

 grows out to form it, and is at first as strongly developed as, and pushes to 

 one side, the continuation of the chief shoot and appears itself to be this con- 

 tinuation. The same process is repeated in the branching of each member except 

 in the case of those which are destined to form organs of attachment or of 

 propagation. The plants are firmly anchored to the substratum by special 

 unbranched members of the thallus which produce at their apex the actual fixing 

 organs, usually termed rhizoids. These members of the thallus, which are the 

 branches marked W in Fig. 14, have a structure and a direction of growth different 

 from what is found in the vegetative twigs. They are, in the mature condition, 

 cell-masses right to the apex, although they are laid down as cell-rows, and they 

 bend towards the substratum. They appear at an early period inserted upon the 

 under side of the branches, and in consequence of this the whole vegetative body 

 has the character of a dorsiventral shoot-system with roots on its under side. The 

 basal branch of one of the short assimilation-shoots shows this best. We must 

 further note that the planes of branching of the assimilation-shoots do not always 

 coincide. In addition to this method of formation of shoots another occurs : 

 isolated unbranched shoots become club-like cell-masses or stichidia, as they are 

 called, which produce the tetraspores. 



1 I say nothing here of the root-threads. 



2 Goebel, Uber einige Siisswasserrlondeen aus Britisch-Guyana, in Flora, Ixxxiii (1897), p. 436. 



