SECT. I 



MORPHOLOGY 



Fio. 8. Dictyota dichotnmn. (jj nut. size.) 



development of external form in the vegetable kingdom is exhibited 

 by such plants as show n DIFFERENTIATION INTO APEX AND P.ASE. 

 The base serves as a point 

 of attachment, while growth 

 is localised at the apex. In 

 this way a growing point is 

 developed at the apex. As 

 an example of such a form, 

 a young plant of the green 

 Alga, Ufoa Laduca (Fig. 5), 

 may be taken. The de- 

 velopment of a more com- 

 plicated external form is 

 represented by the branched 

 filamentous, or ribbon- 

 shaped Algae, in which the 

 origin of new formations is more and more restricted to the apex. 

 An ACROPETAL order of development, in which the youngest lateral 



members are always nearest the 

 growing apex, is clearly demon- 

 strated by the branched fila- 

 ments of the common green 

 Alga, Cladophora glomerata (Fig. 

 6). Still more pronounced is 

 the apical growth in the brown 

 seaweed Cladostephus rerticillatus 

 (Fig. 7). The great variety 

 in the form of the larger Fungi 

 and Lichens, by which they 

 are distinguished as club-, um- 

 brella-, salver-, or bowl-shaped, 

 or as bearded or shrub -like, 

 comes about by the union or 

 intertwining of apically grow- 

 ing filaments. This type of 

 construction is limited to Fungi 

 and Lichens. As the apex itself 

 may undergo successive bifurca- 

 tion, as in the case of Dictyota 

 dichotoma (Fig. 8), it does not 

 always necessarily follow that 

 new members must be formed 

 beneath the original apex. 

 The highest degree of external differentiation among the lower 

 plants is met with in certain groups of red and brown sea-weeds 

 (Rhodophyceae and Phaeophyceae). Many representatives of these 



FlO. 9. Hydi-<ili'ji"tli'nii 



(o nut. sixr.) 



