THE ALG^E 119 



cal lobes, is also apical, and nodes and internodes are developed 

 (Fig. 90, E). The internodes, and sometimes the lateral nodal cells, 

 become much elongated, and form the fluted cortex so conspicuous 

 in Chara. The central nodal cells always remain short, and may 

 give rise to spines or bosses, which encircle the stem at regular 

 intervals. Upon the outer surface of the cells carbonate of lime is 

 often present, deposited in large, irregular masses, which make the 

 whole plant rough and brittle. 



Branches. Besides the leaves, or branches of limited growth, there 

 are also formed branches like the main axis (Fig. 90, A). These 

 always arise in the axil of the oldest leaf of a whorl (occasionally 

 also from the next oldest). In Chara the branch replaces the upper 

 cortical lobe of the oldest leaf of each whorl. 



Roots. The roots consist of slender filaments, also showing apical 

 growth, which grow from the lower stem-nodes. The cells are des- 

 titute of chlorophyll, and the rotation of the protoplasm is exceed- 

 ingly active. 



Reproduction 



No special non-sexual spores occur in these plants. Special bud- 

 like organs are sometimes developed from the old nodes, or upon the 

 roots. These may be single cells, or multicellular bodies, with the 

 cells filled with starch. Such resting-buds, or bulbils, give rise to 

 new plants under favorable conditions. From almost any part of the 

 plant, also, especially in old specimens, there may be developed the 

 so-called " Pro-embryos," simple filaments from which a new plant 

 grows, much as it does in the germination of the resting-spore, and 

 branches with uncorticated base sometimes become detached and form 

 new plants. 



Sex-organs. All of the Characeae show very highly developed 

 sexual reproductive organs, antheridia and oogonia of great com- 

 plexity, and not closely resembling those of any other plants. They 

 are always outgrowths of the leaves, and in their earliest stages show 

 the same type of growth. Their structure is very uniform through- 

 out the order. 



In Chara they ordinarily occur in pairs (Fig. 91, B) on the upper 

 side of the leaf -nodes. A section through the young complex shows 

 that the antheridium replaces a leaflet, and that the oogonium is an 

 outgrowth of its basal node, thus representing a leaflet of a lower 

 order. In Nitella the antheridium is terminal upon a leaf, and the 

 oogonia arise as leaflets about its base (Fig. 94, B). 



Antheridium. The young antheridium (Fig. 91, C-E) consists of a basal 

 node and internode, above which is the globular apical cell separated from the 

 node by an intermediate segment. The globular apical cell divides longitudinally 

 into equal parts, these next divide transversely, and again vertically, so that 



