iOOl.] NATURAL SCIENCES OF PHILADELPHIA. 559 



the island: Phoradendron herterianum Nutt., P. fiavescens Nutt., 

 P. schottu Nutt., P. ruhrum Nutt. The geuus Dendrophthora 

 (formerly included in Arceuthobium) consists of parasites, that 

 arc represented in the Santo Doraingan flora by Dendrophthora 

 cupressoides Eichl., D. grac'ile Eichl., D. opmitioides Eichl. 



Xerophytes. — The writer has briefly alluded to the stretches of 

 country that may be said to be of arid nature in referring to the 

 topography of Santo Domingo. These desertic areas are usually 

 found on the slopes of mountains and in valleys that are sheltered 

 by their position from the prevalent summer rains. These rains 

 may be denominated trade-wind rains, because they owe their 

 origin to the strong evaporation of water within the zone of the 

 trades. If the trade wind encounters a mountainous island, or a 

 bald continental coast, the ascent of air over such obstructions 

 cools it, and the water in the clouds, thus formed, descends as 

 rain. For this reason the windward slopes of Santo Pomingo are 

 well watered, while the leeward slopes are comparatively dry. 

 Again, if the trade winds blow over a land of moderate elevation 

 no precipitation occurs, but the winds reduce its surface to a dry 

 desert by depriving it of moisture. In the Republic of Haiti, as 

 well as in that of Santo Domingo, there are many arid situations 

 which owe their barrenness to just such causes. Consequently in 

 such arid districts we naturally look for a xerophytic flora. The 

 species which exist in such situations are the following: Opuntia 

 tuna Mill., 0. spinossissima Mill., Cereus moniliformis D.C. , C. 

 fjrandiflorus Mill., Nopalea coccinellifera Salm Dyck, Mammillaria 

 simplex Haw., Melocactus communis Link and Otto, Pereskia 

 aculeata Mill. To this list of succulents belonging to the cactus 

 order should be added several other fleshy plants, viz., Agave sobo- 

 lifera Salm Dyck and Aloe vulgaris Lam. The arid hillsides are 

 generally covered, in addition to the xex'ophytes mentioned above, 

 with thickets of Acacia far nesianaWiWd., A. spha;roccphala Cham. 

 and Schlecht., the mezquite, Prosopis juliflora D. C, Yucca 

 aloifolia Linn, and Yucca gloriosa Linn. 



The native flora has been undisturbed on the slopes of the higher 

 mountains inland. Some of the most valuable timber trees have 

 been removed, but cutting them has rather improved the botanical 

 interest of the country, because the smaller plants have thus had 

 a chance^ to grow. Around the dwellings, however, and in the 



