126 VARIATIONS IN NUMBER OF SPORANGIA 
(d) Closely related to (c) is the branching of parts bearing sporangia : 
this may also occur in parts which are in no way morphologically com- 
parable. Branching of strobili is a common feature in Lycopodium and 
Psilotum: branching of the sporophyll is characteristic of most large-leaved 
Pteridophytes: branching of the receptacle of the sorus is common in 
Ferns (Fig. 68): branching of the fertile spike 
b is a marked feature in certain Ophioglossaceae : 
/ branching of stamens is common in the Angio- 
spermic flower, and is to be distinguished from 
the interpolation above mentioned : a somewhat 
similar branching of the sporangiophores has 
probably occurred in the Sphenophylleae. In 
all such cases, though the parts are not mor- 
phologically comparable, the end is attained 
of an increased accommodation for sporangia, 
which consequently may be produced in 
a-d, various examples of fission of increased numbers. . 
the sorus in Hymenophyllum dila- (e) Continued growth and branching, occur- 
tatum. The sporangia, and one flap 4 5 < 2 
of the indusium have been removed, ring in the non-sporangial region, may have 
ese Bae receptacle exposecs the indirect effect of a further increase in the 
opportunities for production of sporangia; for 
not only is the vegetative system thereby increased, which will have its 
indirect effect in increased powers of nutrition, but also a larger number 
of apices are provided, any one of which may take up the character of a 
sporangial strobilus. The continued apical growth in the vegetative region 
is a general feature of Vascular Plants. Branching is profuse in many of 
the strobiloid Pteridophytes: in the Ferns also it occurs, but the effect in 
increasing the opportunities for spore-production is less obvious here than in 
the strobiloid types. In Flowering Plants also the complicated inflorescences 
and the multiplicity of flowers is dependent upon such apical growth, 
together with repeated branchings. 
Factors oF DECREASE. 
(f) Decrease in number of sporangia, by fusion of sporangia which 
previously in the race were separate, has been assumed as an explanation 
of synangial states by various writers: but it can only rarely be proved on 
grounds of comparison that fusion of sporaagia has actually taken place, 
and the best evidence of it comes from the Angiosperms. ‘Thus the fusion 
of the ovules, leading indeed to the obliteration of their identity, occurs in 
certain species of Loranthus, and comparison leaves little doubt that the 
sunken embryo-sacs represent the individual ovules, the identity of which 
is lost as regards external form. Fusion of pollen-sacs is more frequent ; 
good examples, showing various states of the fusion, are found in the 
genus Phyllanthus, and in Cyclanthera; while the unilocular condition in 
