SECT. I 



MORPHOLOGY 



13 



may be taken. The development of a more complicated 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 grow- 

 ing apex, is clearly shown by 



the branched filaments of 



the common green Alga, 



Cladophora glomerata (Fig. 



6). Still moi^e pronounced 



is the apical growth in the 



brown seaweed Cladosfephus 



verticUlatus {Fig. 7). The great variety in the form of the larger 



Fungi and Lichens, by which they are distinguished as club-, umbrella-, 



salver-, or bowl-shaped, or as 

 bearded or shrub-like, comes 

 about by the union or inter- 

 twining of apically growing 

 filaments. This type of con- 

 struction is limited to Fungi 

 and Lichens. As the apex 

 itself may undergo successive 

 bifurcation, as in the case of 

 Didyota dichotoina (Fig. 8), it 

 does not always necessarily 

 follow that new members must 

 be formed beneath the original 



Fii;. S. — Didi/ota diehotoma. (g iiat. size.) 



apex. 



The highest degree of ex- 



among 



ternal differentiation 

 the lower plants is met with 

 in certain groups of Eed 

 and Brown Sea-weeds (Rhodo- 

 phyceae and Phaeophyceae). 

 Some representatives of these 

 classes resemble the higher 

 plants in the formation and 

 arrangement of their members ; 

 Hydrolapathum sanguineum (Fig. 

 9), for example, as is indicated by its name, resembles a species of 

 liumex, and affords an instructive illustration of the analogy of form ex- 

 isting between plants phylogenetically widely distinct from one another. 



Fin. 9. — Hydrolapathum sanguineum. {K nat. size.) 



