II 



thus partaking of the characteristics of both types and excelling in neither, the 

 crop of fruit being meagre compared with the truly pistillate trees. The ash 

 may thus be regarded as approaching or tending towards the fully dioecious 

 state, and a somewhat similar condition may be noted in the common thyme 

 {Thymus serpyllum), the spindle tree {Euonymus Europaus), the holly, &c. 



In such transition plants, although both the essential organs may be repre- 

 sented in the flower, one or other of them is less or more rudimentary and 

 abortive. Thus in a blossom with a perfect fruit -bearing pistil the stamens 

 will be abortive or functionally inert, whilst in the corresponding bloom with 

 fully developed stamens the pistil will be absent or unfertile. But even in 

 hermaphrodite flowers, in which both the organs are present and perfect, self- 

 fertilisation is prevented by their arriving at maturity at different periods. 

 To this arrangement of flowers the term dichogamy is applied, meaning two 

 different marriages. Those in which the stigma matures first, and in which 

 it has passed the receptive stage, and must have been impregnated before its 

 own stamens have shed their pollen, are called proterogynous. Such are seen 

 in the common crocus, where the fimbriated or fringed stigmas may be ob- 

 served protruded for days previous to the expansion of the perianth and the 

 ripening of the stamens, and by the time they are ready to discharge their 

 pollen, the stigmas have lost the power of being fecundated by it. The same 

 conditions occur in the arum [Arum maculatum), the knotted fig wort (Scrqp- 

 hularia nodosa), in several of the plantains (Plantago), but such cases are 

 comparatively rare. The proterandrous condition occurs far more frequently 

 in this, as its name implies the stamens arrive at maturity and emit their 

 pollen previous to the stigmas reaching the receptive stage, when they can 

 be acted upon by it. This is a very general condition, and seems to le 

 widely prevalent amongst the most diverse and distantly related orders of 

 plants. Thus almost every member of the large and eminently natural 

 order Umbelliferce, which includes hemlock, parsley, parsnip, carrot, &c, 

 exhibits these stages. It predominates in the allied order Saxifragacece, and 

 also prevails to a large extent in Composite, whilst representatives occur in 

 every assemblage of plants, this condition being indeed far more common 

 than that in which the two organs arrive at maturity simultaneously. In 

 certain plants, as some of the geraniums and pinks for example, where there 

 are a limited and definite number of stamens, one-half of them ripen and 

 disperse their pollen at an early stage, whilst the other half mature a little 

 later, and just prior to the unfolding of the stigmas, so that there is a chance 

 of their being self-fertilisd. Another obvious way of securing cross-fertilisa- 

 tion is by the stamens and stigma being placed at different levels, so that 

 unaided the pollen could not reach its destination. This is exemplified in, 



