168 



MANUAL OF BOTANY 



Fio. 923. 



The arrangement ot the sporophylls has heen discussed in 

 connection with the morphology of the reproductive organs 

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

 into special branches, caHedfloivcrs, 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, especially in the Pteridophyta, not to be peculiar to the 

 Phanerogams, but to be clearly indicated in the Equisetinae 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 already pointed 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 known 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 

 csJleA pollen-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 parenchymatous cushion already described as the 

 placenta, which in the Gynmosperms is usually on the ventral 

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

 sperms is almost always 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, Oymnospermce, in whicli 

 the ovules are exposed, and Angiospermcc, in which they are 

 enclosed in an ovary. Each of these large groups presents 

 ipiportant pecuharities, the Gymnosperms approaching the 



Fig. 923. Vertical section of flower 

 of Pimpernel, showing axial macro- 

 sporangia. 



