582 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The original position of the nucellus on the leaf-segment is always 

 terminal ; but as soon as the leaf-segment assumes a foliar character, 

 it takes its place on its upper side ; and this is a universal law for 

 vascular cryptogams and phanerogams alike. 



If we now look at the homologies of the reproductive organs out- 

 side the true Filices, we see that the fertile leaves of ci'yptogams with 

 marginal sporocysts, like Botrychium and OpMoglossum, are the proto- 

 type of the carj)ids of Phanerogams with marginal ovules ; and that 

 the fertile leaf of Lycopodium with axillary or subaxillary sporocyst, 

 is the prototype of a carpid with axillary ovule, like Euphorbia and 

 Hanunculus ; and that this is also the case with a carpid with ovule 

 terminal to the axis of the flower, like Polygonum, which, notwith- 

 standing this position, undoubtedly belongs to a carpid of the 

 ovary. 



With regard to the phenomena of coalescence in the various 

 groups, Celakovsky makes the following observations : — 



1. In Angiosperms the trumpet-shaped carpellary leaves of a flower 

 coalesce into a septated ovary. 2. In Marsileacese the cornet-shaped 

 leaf-segments of a fertile leaf coalesce into a 2- or multilocular sporo- 

 carp, the homologue of an integumented ovule. 3. In PsiloteaB the 

 sporangia coalesce with one another as the homologue of a branched 

 but naked ovule. In Marattiacese the numerous emergence-like 

 sporangia coalesce into a multilocular homologue of coalescent nucelli 

 of an ovule. 



As regards the ovules of Gymnosperms, those of Cycadeae are 

 distinguished from the homologous sporangia of the Ophioglossacese 

 only by being invested with an integument ; and their carpellary 

 leaves from the fertile leaves of Ophioglossaceas only by the latter 

 being bifurcate. 



The Coniferse are divided by Strasburger into two main groups : 

 (1) the Araucariaceae (including the AraucarieeB, Abietinese, Cupres- 

 sinese, and Taxodiese), and (2) the Taxacege (including the Taxeae, 

 Podocarpeae, and Cephalotaxeae), which differ so greatly in their 

 morphological characters that they must be considered separately. 



The ovules of the Araucariaceae have only a single integument, 

 and spring from the under side of the carpids which coalesce into a 

 fertile scale and stand in the axil of a bract ; turning towards it, 

 according to the law of inversion, their upper side, and coalescing with 

 it slightly in the Abietineae, very closely in the other families. The 

 phenomena of prolification of the cone show that in the Abietineae 

 the simple scale-like carpels produce each one ovule on its under side. 

 This is a carpel in its simplest possible form, and homologous to the 

 possible case in which the fertile leaf of a cryptogam, e. g. Lycopo- 

 diaceae, should produce a single indusium on its under side. This is 

 also the most probable interpretation of the structure in the Cupres- 

 sineae and Taxodieae, though not so certainly as in the Abietineae. 



In Taxaceae the ovule has two integuments, except in GingJco 

 (Salishuria) and Cephalotaxus, and is inserted on the upper side of the 

 carpel, sometimes higher, sometimes at the base or in the axil of the 

 leaf. The " cones " of the Cycadeae, Podocarpeae, &c., are flowers 



