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A TEXTBOOK OF THEORETICAL BOTANY 



are rightly to be classed as phyllodes, but it is perhaps unwise to extend the 

 theory too far, still more to elevate it into a morphological dogma. 



A comparison of phyllodes with cataphylls is obvious and it would be 

 difficult to draw a clear line between them. Cataphylls generally consist of 

 a leaf base only, and in phyllodes the petiole is usually, though by no means 

 always involved. The term phyllode is, however, by usage, restricted to 

 organs which carry out photosynthetic functions or replace normal leaves 

 in other ways, for instance, as spines ; while cataphylls are, as we have pointed 

 out above, periodic structures limited to certain growth phases of the 



plant. 



The presence of flower buds on true leaves, as distinct from cladodes, is, 



V 



Fig. 984. — Helwingio ntscifolio. Leaves bearing flower buds on the midribs. 



at first sight, a puzzling phenomenon from the morphological standpoint. 

 The best-known example is in Hehvingia riiscifo/ia, a plant often cultivated 

 in greenhouses. A cyme of small flowers appears from the midrib about 

 half-way up on the adaxial leaf surface. A study of the development shows, 

 however, that the flowers originate from the lower of two axillary buds, the 

 upper one of which remains as a normal axillary bud, while the lower one, 

 the flowering bud, coalesces with the young leaf and is carried outwards by 

 it during its development (Fig. 984). 



In one very peculiar case, Eryt/irochiton (Rutaceae), it is the upper bud 

 which is the flowering one and it coalesces with the leaf rudiment above it, 

 so that the flowers appear on the lower side of the leaf above the node to which 

 they properly belong. 



This coalescence of axillary shoots with their subtending leaves is no 



