CONIFERALES 77 



and Selaginella, and in the inner integument the indusiiun of 

 ferns and velum of Isoetes. 



It would seem as though all possible explanations had been 

 suggested. Upon sifting the testimony certain things seem to 

 be fairly clear, and one is that the scale and its ovules in Abie- 

 teae represent a highly modified axillary shoot, corresponding to 

 the characteristic spur shoot of the group. In Taxus, repre- 

 senting the more primitive forms, this ovuliferous spur shoot 

 develops normally, bearing a few leaves, and organizing its 

 ovule in a terminal position, but really in the axil of the upper- 

 most leaf, a fact further emphasized by the lateral and axillary 

 ovule of the allied Torreya. In these cases the ovule is dis- 

 tinctly cauline in origin, and holds the sam^e relation to the sub- 

 tending bract as does the sporangium of Selaginella. Perhaps 

 too much stress has been laid upon the relation of the ovule to 

 the member which produces it. It may be developed from the 

 upper or under surface of the leaf, or from the axis, in the same 

 alliance, but always from periblem tissue. One may expect all 

 of these external expressions of its origin in so ancient and 

 diversified a group as the Conifers, and the desire for absolute 

 uniformity in this regard will probably not be realized. The 

 same spur shoot appears in a somewhat elongated and naked 

 form, in Cephalotaxus, while in Podocarpus it is more or less 

 leafy, the uppermost leaf or two bearing an axillary and stalked 

 ovule. Among the Pinaceae the ovuliferous spur shoot reaches 

 its extreme modification, being represented only by its first two 

 leaves, which have fused to form the ovuliferous scale, and this 

 scale may be more or less coalescent with the subtending bract. 

 Whether those leaves of the spur shoot which are intimately asso- 

 ciated with ovules, either bearing or subtending them, are to be 

 regarded as carpels or as modified outer integuments is a ques- 

 tion we are in no position to answer. It seems simpler to regard 

 them as carpels — that is, leaves modified to bear or subtend 

 ovules, and such a view will be adopted in this book, though not 

 strenuously insisted upon. 



Our knowledge of the development of the megasporangium 

 and of the megaspore in Conifers does not permit generalization, 

 and it is impossible to give an account which will include the 

 whole group. One remarkable feature in the forms studied, 

 which may belong to the group in general, is the extreme slow- 



