1684 A TEXTBOOK OF THEORETICAL BOTANY 



Saxifragaceae 



The family is a large one, containing a number of well-known genera, 

 of which four are native to Britain. They are Saxifraga, Chrysosplerihim, 

 Parnassia and Rihes. Species of Saxifraga are typical of alpine districts, 

 though S. graniilata (Meadow Saxifrage) and S. tridactylites are lowland 

 plants. Chrysospleniiim oppositifoliiim (Golden Saxifrage) grows in wet 

 ditches. Parnassia palustris (Grass of Parnassus) grows in wet grassland, 

 frequently coastal. The genus Ribes includes several species which are 

 cultivated on account of their fruits. R. uva-crispa is the Gooseberry, 

 R. nibruni is the Red Currant and R. nigrum the Black Currant. The genus 

 Ribes is sometimes placed in a separate family, the Grossulariaceae, on 

 account of its woody habit and inferior ovary. 



The family is widely represented in gardens. Many species of Saxi- 

 fraga have been introduced as rock plants and the genus is among the 

 most important to the rock gardener. Many cultivated shrubs also belong 

 to this family among which we may cite Ribes sanguineiim (Flowering 

 Currant), Hydrangea and Philadelphus (Mock Orange) as examples. 



The limits of the family vary considerably in the view of different 

 authorities, Hutchinson, for example, excluding Currants, Hydrangeas and 

 Escallonias as separate families and grouping them in the Resales. We shall 

 not adopt this separation here but take the older and broader view which 

 includes them as separate tribes of the Saxifragaceae. 



The plants are mostly herbs or small shrubs with usually alternate 

 leaves and generally small or moderate-sized flowers which are arranged 

 in complex inflorescences. 



The inflorescence may be either racemose or cymose, though 

 occasionally solitary flowers occur. 



The flowers (Fig. 1543) are hermaphrodite, usually actinomorphic and 

 show a transition from hypogyny through perigyny to epigyny. 



The calyx is composed of five or rarely four sepals, which may be 

 free or united together into a tube. 



The corolla is composed of five or occasionally four petals, which are 

 imbricated in the bud. In Chrvsosplenium the corolla is wanting. 



The androecium is composed of ten, or rarely eight, stamens, which 

 are obdiplostemonous. They may be borne on a prolongation of the recep- 

 tacle above the tip of the ovary, forming a marginal ring. 



The gynoecium is composed of from two to five carpels, often two; 

 and the ovary may be either unilocular or multilocular. The swollen 

 marginal placentas bear several rows of anatropous ovules (Fig. 1544). 

 The ovules frequently possess only one integument. 



The fruit is either a capsule or a berry and contains many small seeds 

 with a copious supply of endosperm. The embryo is minute. 



The family is most characteristic of temperate and arctic regions. Many 

 of the species are cosmopolitan, while others are restricted to certain 

 mountain ranges. There are some ninety genera and 750 species. There 



