300 BOTANY OF THE LIVING PLANT 



The succession of events may often be obscured by vegetative pro- 

 pagation. But, as shown in Chapter XII., this is a mere process of 

 extension, or repetition of the individual sporophyte. It appears as 

 though it extended the cycle, but it does not really introduce any new 

 feature. It may be fitly represented as a supplementary cycle outside 

 the main diagram (Fig. 244). 



The doubling of part of the main cycle indicates sex-differentiation, 

 the male and female developments running parallel. This is a feature 

 which is very prominent in Flowering Plants, and for them the cycle 

 is thus doubled for about three-quarters of its extent. It will be found 

 on applying a similar method successively to plants lower in the scale 

 that in them the sexual differentiation becomes progressively a less 

 parked feature. But meanwhile it is important to note that the 

 extent of this differentiation is not itself constant in Flowering Plants. 



MEGASTORANCIUM. * EHBRYO 



MlGROSPORE. MEGA5PORF.. ZYCOTE. 



FIG. 245- 



In certain plants the flowers are hermaphrodite, as in the Buttercup. 

 The diagram as in Fig. 244 applies to such cases. The sex- differentia- 

 tion appears in them only on formation of the pollen-sacs and ovules, 

 which are in the same flower. But in others the plant is itself 

 either male or female, and the species dioecious, as in the Willow. 

 This condition may be represented by an amendment of the diagram 

 as in Fig. 245. There may be various steps in this further sexual 

 differentiation. For instance, in Lychnis dioica (Fig. 184, p. 236), which 

 is descended from an hermaphrodite stock, the sex-difference appears 

 to be decided by nutrition of the individual, rather than determined 

 in the seed itself. But it is not improbable that in other cases sex 

 may be determined by factors operating directly on the zygote. For 

 us here the point of importance is this. That the stage at which 

 difference of sex is first recognisable in the individual life is not fixed 

 for all Flowering Plants. In hermaphrodite plants it appears only 

 in the several organs of the individual flower. In dioecious plants the 

 difference extends to the whole sporophyte plant. These observations 

 will be of value for comparison with forms lower in the scale of 



