BOTANICAL SUBJECTS. 119 



VIII.— STEM, BRANCH, LEAF, AXD CLADOPHYL. 



What is the genesis of the part of a plant we caU the leaf? 

 It must have had a beginning in its present form somewhere. To 

 meet -vvith its beginnings we must go back to forms which are now 

 whoUy submerged, viz., to seaweeds. Seaweeds had no such 

 organs as leaves, that is, in the sense botanists consider them, but 

 only what they term cladophyls^ reversions or continuations of 

 which we see in land plants, such as Xylophylla, Ruscus, Phyllo- 

 cladus, Phyllocactus, and others. 



In the beginning there was no such thing as a differentiation of 

 stem and leaf. The whole jDlant was either a simple or a com- 

 pound cladopJiyl, that is, a branched stem-leaf. 



In its simplest form the seaweed cladophyl is a cellular 

 expansion, growing out of a corm-like cellular mass, or disk. If 

 we want anything simpler than this, we must go for it to the 

 spore. In Fig. 11 we have the spore of Asperococcus buHosus, 



Fig. 11. Germination of spore of Asperococcus buUosiis, Lamour. (Thuret, 

 " Etud. Phycol.," pi. vi.) 



Lamour. It is a cell which germinates, and throws out root-like 

 or frond-like processes, and floats about, becoming a multicellular 

 body. Eventually it attaches itself to something and leads a fixed 

 life. 



