CUEEENT LITEEATUEE. 59 



the comparison with Acacia phyllodes as indicating that the simpler types 

 of Irid leaf are petiolar phyllodes. She has further come to the conclusion 

 that the same explanation applies to the more complex types of leaf met 

 with in the family, since these prove on examination to be readily derivable 

 from the simpler types, among which the ensiform leaf is regarded as funda- 

 mental. 



The writer considers that leaf-evolution within the family has proceeded 

 on two distinct lines ; on one line the essential feature has been the reduction 

 and ultimately the complete loss of the petiolar region of the phyllode ; on 

 the other line this region, instead of being lost, has been developed and elab- 

 orated. 



Moraea Sisyrinchium may be taken as an example cf the cases in which 

 reduction of the petiole plays the chief role. The greater part of the leaf is 

 flat and dorsiventral, but it ends in a short cylindrical apex, interpreted as a 

 vestigial petiole, while the leaf base forms the main part of the leaf. 



The second line of progression from the simpler types — that of the elabora- 

 tion of the petiolar region — leads us to the more peculiar leaves among the 

 Iridaceae, some of which are so anomalous that it requires a considerable 

 effort to realise that they are leaves at all. The leaf of Gladiolus tristis, for 

 instance, is cruciform in transverse section, while that of Cypella is of an even 

 stranger type, and looks as if it were elaborately folded. The clue to the 

 peculiarities of both the^e leaves is to be found in the transition from leaf- 

 sheath to limb. In both cases the study of the extreme base of the limb 

 suggests that it is a cylindrical petiolar phyllode, modified, however, by 

 invaginations and keels. It is the extreme point to which this invagination 

 is carried which is the main factor in the production of these aberrant leaf- 

 types. 



The writer's examination of the leaves belonging to the two main tribes 

 of the Iridaceae (Iridoideae and Ixioideae) has led her to the conclusion that 

 they can all be explained as phyllodes variously modified from the ensiform 

 type. The third tribe, the Crocoideae, presents at first sight rather more 

 difficulty. But, in this case also, the study of the transition from sheath to 

 limb reveals the fact that we are dealing with a petiolar phyllode. The leaf 

 of Crocus itself is a very peculiar one, and has hitherto been regarded as 

 entirely isolated, and as showing no morphological relation with any other 

 type in the family. But when the Crocus leaf is considered in the light of the 

 Phyllode Theory, it at once falls into line with those of other plants belong- 

 ing to the tribe. The writer interprets it as a petiolar phyllode modified by 

 paired invaginations, and regards its resemblance to an ordinary bifacial 

 blade as purely superficial. 



The members of the Iridaceae have all had the same problem to solve — 

 that of how to transform a petiolar phyllode into something with a more 

 adequate assimilating surface — and they have apparently discovered only two 

 methods by which to achieve it, namely invagination and the development of 

 keels and wings. But the varying way in which they have applied these 

 monotonous methods has resulted in the evolution of an astonishing variety 

 of " pseudo-laminae." 



Printed and Published for the Proprietor by J. B. BUTTRICK at the Methodist 

 Publishing House, Mount Road, Madras. 



