14 MARSILIA QUADRIFOLIA. I'OUR-LEAVED MARSILIA. 



but hints that it probably came from the other side of the Mis- 

 sissippi, which is not covered by his work. It seems, from the 

 description, to be truly the Marsilia quadrifolia. In the " Bul- 

 letin of the Torrey Botanical Club" for 1S72, Dr. J. Ball records 

 it as having been found at Dallas, in Texas, in July of that year; 

 but in a subsequent notice doubt is thrown on its existence in 

 Texas, or indeed anywhere but in tlie one locality at Bantam 

 Lake. It is thought the plants found belong to some other 

 species, perhaps Marsilia vcstita ; but as the descriptions of 

 these two very different species are both given in Prof. Wood's 

 work, it seems probable that the existence of Marsilia quadrifo- 

 lia in the Southwest may be confirmed. 



The great rarity of the Marsilia quadrifolia in the United 

 States has given food for speculation as to its conditions of 

 existence here. It is found native in France, Germany, Siberia, 

 and other parts of Asia, and it seems strange that it should be 

 found indigenous with certainty only in this one locality in our 

 own country. It is of course more than likely that it will yet 

 be found in other places, but it is surely quite scarce enough to 

 favor the question, raised a few years since by Dr. Gray in 

 " Silliman s Journal " : " Is its rarity a sign that it belongs to a 

 very old family about becoming extinct, or is it one of the newer 

 introductions of Nature, which has not yet had time to spread 

 hei-e to any great extent 1 " Geology, and indeed even many 

 facts of modern history, show that numberless forms of plants 

 have become extinct. With this process of extinction going on, 

 the number of species would rapidly diminish, unless others 

 came into existence to supply their places, and yet it is believed 

 that there are quite as many species in existence now as there 

 were at any period in geological history. When we speak of 

 old families of plants dying out, it does not of necessity mean 

 the oldest created forms, for especially among cryptogams, of 

 which our genus is a part, there are some now in existence 

 apparently similar to those found in the earliest fossil remains. 

 It is the same evidently among plants as among races of animals. 



