990 A TEXTBOOK OF THEORETICAL BOTANY 



apparently determined by organismal factors, the fate of the rudiment being 

 decided before its appearance, though the resultant structures may finally 

 differ so greatly that it is not possible to homologise their parts. 



The cataphvlls of the winter bud mark the base of each year's shoot- 

 generation during the growth of a perennial plant. Similarly the base of 

 the first shoot in the seedling frequently bears cataphylls. Following the 

 cotyledons a succession of reduced leaves may be produced, increasing in 

 size at each node and leading eventually to the mature leaf form. Unlike 

 the bud scales these cataphylls are separated by internodes, the length of 

 which increases upwards on the stem. 



Cataphvlls, like other leaves, usually subtend axillary buds, which are, 

 however, of reduced size and are generally dormant. If they are stimulated 

 to growth, as, for example, by severe pruning, they form dwarf and slow- 

 growing shoots, or spurs, on which flowers are borne. 



A third type of scale formation is that from the stipules of leaves. Many 

 buds have scales of this type, for example, Almis, where the bud is covered 

 by three scales, two being the stipules of the outermost leaf and the third 

 being one stipule of the second leaf. Other conspicuous examples are Magnolia 

 and Liriodendron, in which the stipules fall off when the buds open and their 

 protective function is finished. In the buds of the Oak and Beech there may 

 be a considerable number of such stipular bud scales, each of which is a 

 double structure formed of a pair of stipules, the lamina being reduced to a 

 microscopic point. Only the two outermost scales are simple. 



Hypsophylls originally included all the floral leaves, petals and sepals 

 as well as bracts, but the term is now generally limited to the latter. Bracts 

 may be green organs with the same assimilatory capacities as foliage leaves, 

 or they may act as protective coverings to the flower or inflorescence buds 

 (Fig. 978), and in some cases they may be specially coloured and serve the 

 biological end of increasing the conspicuousness of the flowers. If a hypso- 

 phyll subtends an axillary structure, this is usually, though not invariably, 

 a flow^er or a flowering branch and its peculiarities of form seem to be linked 

 with this fact, since in cases where an inflorescence produces fresh vegetative 

 shoots, the normal foliage generally reappears on these. The term bract is 

 usually applied to a hypsophyll subtending an inflorescence, and the term 

 bracteole to one which subtends a single flower, but the distinction is not 

 universally applied, and the term hypsophyll itself, which merely serves to 

 unite the two categories of organ, is not, therefore, of much general utility. 



Like the cataphylls, the hypsophylls are often connected with the normal 

 leaves by intermediate forms which make a sharp line of division impossible, 

 and again like the cataphylls, they may arise in three different ways. Firstly, 

 by a reduction in development of the entire leaf ; secondly, and more com- 

 monly, by a reduction or abortion of the lamina and petiole, and a correspond- 

 ingly enhanced development of the leaf base. This may often be perceived 

 by a comparison of the venation with that of the normal leaf. The leaf base 

 usually has a distinctive venation, different from that of the lamina, even when 

 it is coalescent with it, and this tvpe of venation will be found to correspond 



