458 PRIMULALES— GENTIANALES 



the insect's body in fringe-like masses (Fig. 327, D). One of 

 the lower basidiomycetes {Exobasidiiim) infests the leaves and 

 flowers of the azalea and other genera, causing large watery 

 outgrowths that are often eaten under the impression that they 

 are the fruit of the plant. The members of this order are 

 adapted to a wide range of conditions though more characteris- 

 tic of north temperate and arctic regions where they consti- 

 tute the conspicuous features of the tundras, bogs, heaths and 

 moors. These plants are often characterized by their thick 

 leathery, evergreen leaves of pronounced xerophytic character 

 and their common distribution in wet moors and bogs presents 

 a most puzzling problem in the association of plants. Many of 

 the heaths have been cultivated from very early times and they 

 have lent themselves so readily to crossing that perhaps no order 

 furnishes so many forms for decorative and landscape effects. 

 Several yield valuable fruits, as the blueberries, huckleberries 

 and cranberries. 



151. Orders of a Higher Type than the Ericales. — The prim- 

 rose order (Primulales) forms a very natural transition from the 

 Ericales. As the next step in advance, we note the slight ad- 

 hesion of the stamens to the corolla (Fig. 328, A) and their 

 frequent reduction in number. The occurrence of staminodia, 

 page 405, in certain forms marks the first transition to the 

 reduction of the number of stamens. The pistil is generally 

 composed of five carpels forming a capsule without partitions 

 (unilocular) and containing a central placenta, bearing numerous 

 seeds, that is attached only to the base of the ovary (Fig. 328, A). 

 This is the so-called free central placenta and only occurs else- 

 where in the small bladderwort family of aquatics. This order 

 includes the loosestrife (Lysimachia and Steironema), star flower 

 (Trientalis), shooting star {Dodecatheon) and cultivated forms of 

 the cyclamen and primroses. 



Proceeding to the gentian order (Gentianales), it will be 

 noted that the flowers are variable and not as clearly character- 

 ized, the corolla being sometimes wanting or polypetalous. The 

 reduction of the stamens to a single whorl and the pistils usually 

 to two in number indicates points of advance that are to be 



