MORPHOLOGY 



155 



attain a mature condition, a distinguishing feature of the ontogeny 



of plants as compared with animals (p. 4). In more simply 



constructed plants the grow- 

 ing point consists of a single 



cell. This assumes more 



and more the character of 



an APICAL CELL from which 



all the organs of the plant 



take their origin ; thus, in 



the case of Cladostephus ver- 



ticillatus (Fig. 7), the many- 

 celled main axis terminates 



in a single conical cell which, 



by transverse and longi- 

 tudinal divisions, gives rise 



to the cellular system of 



the whole plant. Its lateral 



branches are likewise formed 



from similar apical cells, 



which develop, in regular 



acropetal order, from certain 



of the lateral cells of the 



parent stem, and determine 



the character of the branch- 

 ing. Flat, ribbon-like 



plants also, such as Dicty- 



ota dichotoma ( U6 ) (Fig. 8), 



may have conical but correspondingly compressed apical cells (Fig. 



162 A], from which segments are cut off by concave cross walls, 



and become further divided by subsequent 

 longitudinal walls. The dichotomous 

 branching so apparent in Dictyota is pre- 

 ceded by a longitudinal division of the 

 apical cell into two equal adjoining cells 

 (B, a, a). By the enlargement and con- 

 tinuous division of these two new apical 

 cells the now bifurcated stem becomes 

 prolonged into two forked branches. In 

 represent .,. other ribbon-like Algae, on the other hand, 

 tion of the apex of Metzgena fur- and in similarly shaped Hepaticae, as in 



cato in process of branching, viewe.1 Metzger i a an d Awum ( 147 ), the apical cell 



from the tlorsal side, a, Apical . f . , v (' 



cell of parent shoot ; 6, apical cell IS wedge-shaped (V Ig. 1 63), and the SUCC6S- 



of daughter shoot. (After KNY, s i ve segments are cut off alternately right 

 and left by intersecting oblique walls ; 



from these segments the whole body of the plant is derived by further 

 division. The apparently strictly dichotomous branching of Hepaticae 



l-'ic;. li'c'. The growing point of Di<:tyotH dichotoma, show- 

 ing the dichotomous branching. A, Initial cell. (After 



E. DE WlLDEMAN, X 500.) 



