DEVELOPMENT OF PLANTS 



445 



must be thorough in order not to spread the infection. AppHca- 

 tions of alcohol containing sugar of lead (50 or 70 per cent, 

 alcohol) are also recommended, which treatment is followed by 

 thorough washing in alcohol. As in the preceding orders, the 

 lower members of this group are characterized by a regular alter- 

 nation of the members of each whorl, but in the higher types the 

 sets of organs vary in number and the flowers become irregular, 

 as in the horse-chestnut and balsam weed or touch-me-not. 



Fig. 320. Two poisonous species of the Sapindales: A, Rhus vernix, poison 

 sumac. B, Rhus radicans, poison ivy. 



146. Orders Suggestive of the Sapindales. — The geranium 

 order, Geraniales, shows essentially the same type and range of 

 variation in the flower as the Sapindales, but there is this rather 

 singular diff^erence, namely, that the ovules, usually pendulous, 

 are always turned away from the axis of the ovary with micro- 

 pyle directed upwards, while in the Sapindales the opposite ar- 

 rangement is to be found, micropyle pointing down (Figs. 318, D\ 

 321, D). This order ranges from the regular flowers of the 

 oxalis, flax and geranium families to irregular forms like the 

 nasturtium, milkwort {Poly gala), etc. Many of these plants are 

 known by their peculiar juices, oils, gums, as in the spurges 

 {Euphorbia), castor bean {Ricinus), citron, lemon, orange, etc. 

 The fruit of the lemon and orange is a berry in which the outer 

 part of the ovary becomes leathery. The juicy pulp, which en- 



