62 PLANT-LIFE ON LAND [OH. 



In the Common Club-Moss (Lycopodium Selago), 

 after an initial vegetative growth in which all the 

 leaves of the young plant are sterile, the shoot settles 

 down to a condition which is shown in Fig. 12. The 

 small and simple leaves appear all alike in size and 

 texture, being clearly nutritive in function. The 

 whole shoot is uniform throughout its length, except 

 that it is marked off into successive zones which are 

 alternately sterile and fertile. In the former a single 

 sporangium is present in the axil of each leaf : in the 

 latter the sporangia are absent. But at the limits of 

 the fertile zones there are smaller abortive sporangia, 

 while occasionally an isolated sporangium, or two or 

 three of them, may be found within an otherwise 

 sterile zone. When it is remembered that spore- 

 production was constant throughout descent, such 

 facts point very directly to the conclusion that there 

 existed at first a shoot which was both nutritive and 

 propagative, and that this Club-Moss shows those 

 functions only partially separated, the sporangia 

 being imperfect or entirely suppressed in the sterile 

 zones, while the fertile zones maintain their pristine 

 state. But in the great majority of the Club-Mosses 

 the sporangia are associated with the leaves at the 

 end of the shoot only, forming a cone or strobilus. It is 

 plain that in them the differentiation has been carried 

 out more perfectly. Such cones are the prototypes 

 of Flowers, while the sterile region below represents 



