168 



MANUAL OF BOTANY 



Fig. 923. 



The arrangement ot the sporophylls has been discussed in 

 connection with the morphology of the reproductive organs 

 (Vol. I. Chapter II,), where their collection with other leaves 

 into special branches, called flowers, has been fully treated of. 



This development of a special branch system in connection 

 with the occurrence of spores has been seen in the previous 

 groups, especialh^ in the Pteridophyta, not to be peculiar to the 

 Phanerogams, but to be clearly indicated in the Equisetinse and 

 the Lycopodinse. What is, however, exceptional in the lower 

 forms becomes in the Phanerogams a constant and characteristic 

 feature of their life. 



It has been ah-eady pomted out that in the Phanerogams the 

 sporangia, though usually borne upon leaves, are sometimes axial 

 in their origin {fig. 923). This is seen in the case of both micro- 

 sporangia and macrosporangia. 

 When borne upon leaves, these 

 are kno^\Ti as microsporophylls 

 and macrosporophylls respec- 

 tively. The microsporophylls 

 are also called stamens, or 

 staminal leaves ; while the macro - 

 sporophylls are termed carpels, 

 or in some cases carpellary 

 leaves or scales. 



The microsporangia, often 

 CQ^edii)ollen-sacs, are situated at 

 different places upon the stamen 

 or staminal leaf. In the Gymno- 

 sperms they are upon the under side ; in the Angiosperms 

 upon both surfaces. The macrosporangia, or ovules, arise from 

 a special parenchjTuatous cushion already described as the 

 2)lacenta, which in the Gj-mnosperms is usually on the ventral 

 surface of the sporophyll or carpellary scale, but in the Angio- 

 sperms is almost alwaj^s a development of the margin of the 

 carpel. The carpel, or frequently the collection of carpels in a 

 flower, forms by various cohesions at their bases in the latter 

 case a closed chamber or ovary in which the macrosporangia are 

 concealed. 



Based on this latter point we have the classification of the 

 Phanerogams into two large divisions, Gymnosjperince, in which 

 the ovules are exposed, and Ang i o sjyer 772 ce, in which they are 

 enclosed in an ovary. Each of these large groups presents 

 important peculiarities, the Gjminosperms approaching the 



Fig. 923. Vertical section of flower 

 of Pimpernel, showing axial macro- 

 sporangia. 



