i6i6 A TEXTBOOK OF THEORETICAL BOTANY 



The primitive nature of the Magnohaceae is well shown by the spiral 

 arrangement of the floral parts and in various anatomical features. The 

 remarkable geographical distribution of the family, which at the present day 

 is entirely absent from Europe, Africa and to a large extent Australasia, has 

 been interpreted as evidence of the antiquity of the family. This is further 

 supported by the evidence of leaves, attributed to Magnolia and Lirioden- 

 dron, found in the Tertiary beds of both Europe and Greenland, which 

 suggests that at one time the group was probably distributed all over the 

 northern hemisphere, whence, as in the case of Drimys, it spread south- 

 wards. 



The Annonaceae are essentially tropical in distribution. They are a 

 large family with eighty genera and over 800 species, consisting of trees 

 or shrubs, mostly occurring in the Old World. Oil passages are present in 

 the stems. The flowers are regular and hermaphrodite, with three whorls 

 of three perianth segments, the outer two being sepaloid. The stamens 

 and carpels are numerous and spirally inserted, each of the latter containing 



Fio. 1470. — Annona cherimolia. Aggregate fruit. (By courtesy 

 of the Florida Field Experimentation Station.) 



numerous anatropous ovules. The endosperm of the seeds is bulky and 

 is ruminate, that is to say it is penetrated by extensive folds of the inner 

 testa. This condition is one of the distinguishing marks of the family. 

 The fruit is either an aggregation of berries or a pseudocarp in which the 

 receptacle as well is involved (Fig. 1470). The chief interest in the family 

 lies in these fruits, which, though they contain large seeds, are in many 

 cases sweet and succulent, and in consequence are largely cultivated in 

 tropical countries. Among the better known of these we may mention the 

 Cherimoya {Annona cherimolia), Custard or Sugar Apple {A. squamosa), 

 Soursop {A. miiricata), Bullock's Heart [A. reticulata), and llama {A. 

 diver sifolia). Recent analysis shows that these fruits contain about 18 per 

 cent, of sugar. 



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