ANATOMY 31 



tion of the leaf strands to the vascular tissue of the 

 main stem is a very important factor. In the modern 

 higher plants the primary vascular strand passing up 

 the stem passes directly out to the leaf stalk, so that 

 the leaf strands and those from the stem are the same 

 and form one system. In some of the lower plants, 

 and in many of the fossils, this does not appear to be 

 so, and it is possible that in the early forms the stem 

 had a system of vascular strands of its own which helped 

 to complicate matters for those who theorise. 



