Strobilus in Archegoniate Plants. 365 
be regarded as primary, the vegetative tissues as secondary, in 
point of evolutionary history. 
2. Other things being equal, increase in number of carpo- 
spores is an advantage ; a climax of numerical spore- 
production was attained in the homosporous Vascular 
Cryptogams. 
3. Sterilization of potential sporogenous tissue has been 
a wide-spread phenomenon, appearing as a natural consequence 
of increased spore-production. 
4. Isolated sterile cells, or layers of cells (tapetum) served 
in many cases the direct function of nourishing the developing 
spores, being themselves absorbed during the process. 
5. By formation of a central sterile mass (columella, &c.) 
the spore-production was, in more complex forms, relegated 
to a more superficial position. 
6. In vascular plants, parts of the sterile tissue formed 
septa, partitioning off the remaining sporogenous tissue into 
separate loculi. 
7 . Septation to form synangia, and subsequent separation 
of the sporangia, are phenomena illustrated in the upward 
development of vascular plants. 
8. Such septation may have taken place repeatedly in the 
same line of descent. 
9. The strobilus as a whole is the correlative of a body of 
the nature of a sporogonial head, and the apex of the one 
corresponds to the apex of the other. 
10. Progression from the simpler to the more complex type 
depended upon (a) septation, and (b) eruption to form super- 
ficial appendicular organs (sporangiophores, sporophylls) upon 
which the sporangia are supported. 
1 1. By continued apical growth of the strobilus, the number 
of sporophylls may be indefinitely increased. 
12. The sporophylls are susceptible of great increase in size, 
and complexity of form ; in point of evolutionary history, small 
and simple sporophylls preceded large and complex ones. 
13. In certain cases foliage-leaves were produced by sterili- 
zation of sporophylls. 
