ORIGIN OF STERILE REGION—SECONDARY 161 
present day will justify the assumption that in the evolutionary story 
sporangia originated indiscriminately upon pre-existent vegetative organs. 
My own opinion is that it does not, for a careful examination of such 
‘cases and comparison of them with the general type to which the plants in 
question belong shows that they are exceptional, if not indeed of the nature of 
monstrosities. It is clear that promiscuous formation of sporangia in 
present-day forms is possible, and that it does at times occur, but it 
‘does not follow that this was a general mode of their origin in past 
times. 
An essential fact bearing upon the question in point is that spore- 
production is a constantly recurring event in Archegoniate Plants. There 
is good reason to believe that it has found its place in every normally 
‘completed life-cycle throughout their descent. Cytologically it is now 
seen to be the natural complement of the sexual process. Taking all 
types of Archegoniate Plants into our view, including the more recent 
Flowering Plants as well, there is reason to believe that spore-production 
was the initial function of the sporophyte, and that it has been continued 
and repeated throughout descent. If this be admitted, how can the 
strobilus, or the flower—the part bound up with that primary function 
of spore-production—be the result of metamorphosis of a vegetative shoot, 
the leading function of which is secondary? The conclusion to be derived 
from broad comparison will be the direct converse: viz. that vegetative 
parts in the sporophyte have originated by change of parts originally 
fertile. 
* But in order to carry conviction that this conclusion is correct, it will 
be incumbent on those who hold it to bring forward evidence bearing on the 
origin or increase of the vegetative system, which we see at the present 
day preceding spore-production in the history of the individual life. It 
has already been shown in Chapter VII. that s¢erclisation of individual 
‘sporogenous cells, that is, their conversion into cells having a vegetative 
function, is common. It is found in the sporangia of Vascular Plants, 
but it is in the sporogonia of Bryophytes that it has been recognised as 
specially effective in adding to the vegetative system. The sporogonium 
of Aneura (Fig. 86) has already served as an example, while reference to the 
writings of Goebel (Organography, pp. 326-329, Engl. Ed., p. 103), shows 
how fully sterilisation has already been realised, and accepted as a source 
of increase of the vegetative system in the Bryophyta. Similarly, in 
Vascular Plants it has been shown above, that sterile cells of a sporo- 
genous group may be converted into vegetative tissue of a septum. Such 
examples’ indicate how sterilisation of individual cells may be effective in 
increasing, and perhaps in the first instance even in originating, the vege- 
tative system. 
A second factor, which has been specially effective in contributing to 
the increase of the vegetative system in the more differentiated types of 
sporophyte, is the abortion of sporangia, or of Sporangium-bearing parts. 
is 
