DEVELOPMENT OF PLANTS 



427 



vine or sometimes a shrubby plant with leaves divided into three 

 leaflets and with nut-like fruits (Fig. 320, B), while the poison 

 sumac is an erect coarse shrub ten to fifteen feet high, with large 

 pinnate leaves with reddish petioles and fruit clusters, as in the 

 poison ivy (Fig. 320, A). As in the preceding orders, the lower 



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

 poison sumac. B, Rhus radicans, poison ivy. 



members of this group are characterized by a regular alternation 

 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. 



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 difference, 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 



