227 
Azolla, where an envelope occurs around the macrospo- 
range as a new entirely independent annular covering. 
» lhough it may be premature to attempt to define in 
terms of stimulus and response the precise sequence of 
events that leads up to encasement, it will be readily 
admitted that a new departure such as the inception of 
the seed habit (where provision has to be made for the 
increased nutrive drain involved by the retention of the 
gametophyte) would be accompanied by nutrive distur- 
bances that might easily favour the appearance of new 
formations” (p. 104). 
Now that I have endeavoured to give some of the most 
important theories, concerning the origin and value of the 
integument, and to show how much these conceptions 
differ from one another, some questions are obvious viz. 
1. The integuments of the Pteridosperms, Gymnosperms 
and Angiosperms are they comparable with one another, 
or is their origin polyphyletic. 
2. If the integuments are homologous organs, are they 
also homologous with the indusium of the Ferns. 
3. Is the integument composed of several units, which 
may be evident as ribs or sutures or as slips at the micropyle. 
4. If the integument is composed of units, what is their 
value. 
It is the intention of the present paper to try to 
solve these questions or at least to throw a new light on 
these problems. I shall therefore describe in the second 
chapter some of the most characteristic fructifications pro- 
vided with an integument, attempting to mention the results 
of each investigation as objectively as possible, without 
falling into any subjective supposition. 
Though in the descriptions of the palaeobotanical seeds 
no new observations are recalled, | have collected the 
data from the literature in the same order as the others, 
because they were not complete in any textbook. 
