120 VARIATIONS IN NUMBER OF SPORANGIA 
plants it is possible to recognise certain methods of numerical change of 
sporangia, now or previously operative: these may either lead to pro- 
gressive zcrease in number, or to decrease in number. Under these two 
heads the following table shows the several methods of change in number 
of sporangia of which evidence has been found in living plants, but it is 
possible that the table is not exhaustive : 
J. INCREASE IN NUMBER OF SPORANGIA. 
(a) By septation, with or without rounding off of the individual sporangia. 
(4) By formation of new sporangia, or of new spore-bearing organs, which 
may be in addition to, or interpolated between those typically 
present. 
(c) By continued apical or intercalary growth of the parts bearing the 
sporangia. 
(dz) By branching of the parts bearing the sporangia. 
(e) Indirectly, by branchings in the non-sporangial region, resulting in 
an increased number of sporangial shoots: this is closely related 
to (c) and (d). 
II. DEcREASE IN NUMBER OF SPORANGIA. 
(f) By fusion of sporangia originally separate. 
(g) By abortion, partial or complete, of sporangia. 
(2) By reduction or arrest of apical or intercalary growth in parts bearing 
sporangia. 
(2) By fusion of parts which bear sporangia, or arrest of their branchings. 
(/) Indirectly, by suppression of branchings in the non-sporangial region, 
resulting in decreased number of sporangial shoots: this is closely 
related to (#) and (2). 
Each of these factors of variation will now be discussed, and examples 
of them adduced. At the moment the object is only to recognise that 
such modifications of number of sporangia are or have been operative 
in actual cases, not to estimate the relative prevalence of any one: for 
it is necessary first to distinguish the factors of the problem. 
Factors OF INCREASE. 
(a) Increase in number of sporangia by seffation, resulting in a plurality 
of loculi, where previously in the race the septa were absent, is shown 
in the septate anthers of various families of Angiosperms (Onagraceae, 
Mimoseae, Rhizophoreae, Myrsinaceae, Loranthaceae, etc.). The details 
have already been sufficiently described in Chapter VIL, p. 97. The 
argument that septation has occurred is in many of these cases quite 
conclusive : thus the plurilocular anthers of certain genera of the Onagraceae 
