56 PART I. MORPHOLOGY. 



In heterosporous plants it is commonly the case that the two 

 kinds of sporangia are borne together on the same axis of the 

 sporophore ; that is, they are included in the same flower (e.g. Sela- 

 ginella, most Angiosperms), but they are frequently confined to 

 distinct axes, as in the Gymnosperms, and in some Angiosperms 

 (e.g. Beech, Birch, Oak, Walnut, etc.) ; these distinct flowers 

 are distinguished, according to the kind of sporangia which 

 they respectively bear, as micro sporangiate or macrosporangiate ; 

 in some cases one individual bears exclusively microsporangiate, 

 and another exclusively macrosporangiate flowers, as in the Hemp, 

 the Yew, etc. 



(c) The Sporophylls. In many cases, most Ferns and Lycopo- 

 dinae, for example, the sporophylls are similar to the foliage- 

 leaves, differing only in that they bear sporangia ; but more com- 

 monly the sporophylls are distinguished by some peculiarity in 

 form or structure. Thus in the Flowering Fern (Osmunda rcgalis) 

 the sporophylls differ from the foliage-leaves in that no green 

 leaf-tissue is developed in them; and in the Phanerogams they 

 differ widely from the foliage-leaves. 



The distribution of the sporangia among the sporophylls in 

 heterosporous plants is an important point. In the Hydropteridese 

 (Rhizocarpse), both the microsporangia and the macrosporangia 

 are borne by the same sporophyll ; but in all other heterosporous 

 plants they are borne by distinct sporophylls, which may be dis- 

 tinguished respectively as microsporophylls and macro sporophylls. 

 In the Phanerogams the microsporophyll is termed a stamen ; the 

 macrosporophyll, a carpel ; but there is no reason for applying 

 special terms to this group of plants. 



In heterosporous plants, both kinds of sporophylls are gener- 

 ally present in one and the same flower : when, however, the 

 flower includes only microsporophylls, it is termed microsporophyl- 

 lary or staminate ; and when it includes only macrosporophylls, it 

 is termed macrosporophyllary or carpcllanj. 



In some cases the sporangia are borne, not upon, but in close relation 

 with, a leaf, which is nevertheless regarded as a sporophyll. Thus, 

 in Selaginella, the sporangium is in the axil of the sporophyll. Again, 

 the leaves which invest the macrosporangia (ovules) of Polygonacea?, 

 Primulaceae, etc., are termed carpels, though they do not actually bear 

 the sporangia. 



The distribution of the sporangia on the sporophyll is various. 

 They may be borne exclusively on the under (dorsal) surface, 



