202 PRINCIPLES OF PLANl'-l'IfiEATOLOGY. 



ovule of Trifolium repens* its similarity to the bilobed 

 funicular lamina enclosing the inner integument is 

 obvious : the two structures are to be regarded as 

 homologous although naturally presenting differing 

 degrees of development of the respective parts. In 

 Dichsonia the sorus is also terminal to the leaf-segment, 

 but the indusium is here tw^o-lipped instead of cup- 

 shaped. In Bavallia and Microlepia the first stage in 

 the projection of the sorus on to the lower surface is 

 seen, this being caused by the elongation of the upper 

 side of the indusium, which becomes green and is 

 (in part) an extension of the pinnule-segment (the 

 outer integument). The final stage is seen in Gystoj)- 

 teris, where the sorus with the lower lip of the indusium 

 is projected completely on to the lower surface of the 

 pinnule-segment (PI. XL VIII, fig. 15). 



In Glbotium and Cyathea there is a distinct cup- 

 shaped indusium situated on the lower surface of the 

 segment; in the former this is at first terminal and 

 marginal, becoming subsequently displaced into an 

 inferior position ; in the latter it is inferior from the 

 first (PI. XLIX, fig. 3). In these two cases we have 

 the exact counterpart of an inner integument situated 

 on the lower surface of a "basal lamina" or prolife- 

 rated outer integument or funicle such as occurs in 

 Shymhrium Alliaria and Reseda (PL XLIX, fig. 4). 

 PI. XLIX, fig. 5, shows the same thing in a perianth- 

 leaf of a tulip. Completely foliaceous ovules are 

 shown in PI. XLIX, fig. 1 (Aqiiilegia), and fig. 2 

 (IVifiilium) . 



The present writer is in complete harmony with 

 Celakovsky's view of the subject. But, owing to our 

 utter ignorance of the nature of the original ancestry 

 of the Angiosperms, it is impossible to know the exact 

 form and structure of the sporophyll and its parts out 

 of which the modern carpel and ovules became diffe- 

 rentiated ; this more especially concerns the primitive 



* With which it is more comparable than with the normal ovule. 



