THE DICOTYLEDONES 



1823 



430 species and Hydrocera. They are all herbs, with watery translu- 

 cent stems and alternate leaves. The flowers are hermaphrodite and 

 zygomorphic, a spur being formed by the greatly enlarged posterior sepal. 

 The slender pedicel is often twisted so that the spur becomes anterior, that 

 is to say, the flower is resupinate. Cleistogamic flowers are often pro- 

 duced. 



The chief interest in the family is the explosive nature of the capsule 

 at the time of maturity. In Impatiens noli-tangere (Fig. 1725) the capsule 

 has a fleshy pericarp, the cells of the outer layer of which are highly turgid. 



Fig. 172s. — Impatiens nali-taniiere. A, Shoot with capsules, two of which have dehisced. 

 B, Ripe capsule. C, Capsule dehiscing. The carpel valves roll up elastically and 

 throw off the seeds with considerable force. 



This puts a great strain on the whole structure. Dehiscence is septifragal 

 and is started by the least touch on the ripe fruit. The valves roll up 

 inwards with great violence, starting at the base, with the result that the 

 seeds are shot out in all directions. 



/. noli-tangere is the only British species, though /. fiilva, a North 

 American species with orange flowers, and /. roylei, a Himalayan species 

 with pink flowers, have become naturalized. /. bahamino (Balsam), an 

 East Indian species, is often grown in gardens. Hydrocera is represented by 

 a single species, a marsh plant found in India and Java. 



The Erythroxylaceae are a small family with two genera and 200 species. 

 They are shrubs or trees with ahernate, entire leaves. The only important 

 member which we must mention is Erythroxyhim coca. The leaves ot 

 this plant are of extreme economic importance as the chief source of 

 cocaine. 



The Malpighiaceae are a family of woody plants found mainly in 

 South America. There are some fifty-five genera containing about 650 

 species (Fig. 1726). Many of them are climbers and form lianas with very 

 complex and abnormal anatomy. The simplest of these abnormalities is the 

 development of phloem islands in the xylem, which occurs in all the species 



