16.] CHAPTER II. SPECIAL MORPHOLOGY OF THE MEMBERS. 79 



In most cases the sporangia are free on the surface of the 

 sporophyll; but in some cases they are enclosed in a cavity formed 

 either by the infolding and junction of the margins of the sporo- 

 phyll, or by the junction of the margins of adjacent sporophylls. 

 The sporangia of the Marsiliacese are thus enclosed by the sporo- 

 phyll, as are also the macrosporangia of all Angiosperms. In the 

 latter group the resulting structure is termed the ovary. 



(d) The Hypsophylls (Fig. 36, p. 57). Under this common term 

 are included bracts and perianth- leaves. 



Bract. This term is generally applicable to the leaves, other 

 than the sporophylls and perianth-leaves, which are borne by the 

 rhachis or branches of the inflorescence: those which are borne 

 on the pedicels of individual flowers are, however, distinguished as 

 bracteoles or propkylla. 



The bract is frequently not distinguishable from a foliage-leaf, 

 but it may be reduced to a scaly leaf, or it may be very large and 

 even highly coloured, when it is said to be petaloid. An example 

 of the occurrence of bracts in the Pteridophyta is afforded by 

 Equisetnm, where there is a whorl of small bracts, forming what 

 is known as the ring, just below the cone or flower. In some 

 Monocotyledons (e.g. Palms, Arums, etc.) there is a large bract, 

 termed a spathe, which invests the whole inflorescence: it is usually 

 not green in colour, as in the Trumpet Lily (Zantedeschia cethiopica} 

 where it is white. In some cases the bracts are arranged in whorls 

 round the inflorescence (e.g. Composite) forming an involucre. 



The bracteoles sometimes form an investment, termed an epicalyx, 

 to the flower (e.g. Malva, Camellia, etc.). 



The Perianth-leaves are leaves developed in immediate relation 

 with the sporophylls, or with the sporangiferous axis, of a flower, 

 to which they form a protective or attractive investment termed 

 the perianth. A perianth is present only in Phanerogams, and is 

 confined almost exclusively to the Angiosperms : the Gnetaceae are 

 the only Gymnosperms in which it is represented. The leaves may 

 be arranged in a single whorl, or in two or more ; or they may be 

 all alike, either green and inconspicuous, or of other bright colours 

 and conspicuous ; most frequently the leaves of the outer whorl 

 (sepals constituting the calyx) are small and green in colour, being 

 especially protective in function, whilst those of the inner whorl 

 (petals constituting the corolla} are large and brightly coloured, 

 being especially attractive in function. (For further details, see 

 The Flower, Part III). 



