1158 A TEXTBOOK OF THEORETICAL BOTANY 



calyx, may be taken over by bracts, which surround and enclose the young 

 flower in a manner exactly analogous to that of a normal calyx. 



Fig. 1 1 30. — Phy salts peruviana. Persistent, inflated 

 calyces enclosing the berry fruits. 



A peculiar physiological modification is that known as a water calyx, 

 in which the calyx forms a closed sac loosely enfolding the flower bud, 

 and filled with water which is secreted from glands on the inner surface of 

 the sepals, so that the young flower is immersed and completely protected 

 from desiccation. These calyces are especially characteristic of tropical 

 plants, particularly in the families Bignoniaceae and Solanaceae. Analogous 

 water calyces enclosing the young fruits are found in some members of the 

 Convolvulaceae. 



The calyx has a generally protective function in the bud stage of the 

 flower but in some genera the sepals persist into the fruiting stage, e.g., 

 Rosa, Clerodendron, Ceratopetahun, when they may fulfil other functions 

 in connection with fruit dispersal. Marking the change of function there 

 are very often changes of colour or consistency, correlated with the changes 

 which fertilization brings about in the gynoecium. 



Sepals occasionally bear stipules, which appear to form an outer zone 

 of smaller sepals, known as the calyculus. The Strawberry and a number 

 of related genera in the Rosaceae have a calyculus of five segments alter- 

 nating with the five sepals, and formed of stipules fused laterally in pairs, 

 two to each sepal. Such structures should be distinguished from a true 

 epicalyx, in which, as in Maha, the outer zone is composed of small 

 bracts in a whorl. The difference between such a whorl of bracts and an 

 involucre (see p. 1 142) is only a matter of degree, the bracts which form an 

 involucre being rather less close to the calyx, as in Anemone hepatica and 

 Dianthus, and frequently united to each other. We do not consider that a 

 clear distinction is possible, but the two terms may be retained, as they 

 are descriptively convenient in distinguishing cases where the bracts appear 



