THE AMERICAN BOTANIST. ill 



conducting numerous experiments to discover the cause of the 

 trouble if possible. A clue was obtained when it was discovered 

 that even the ash of some of the plants was poisonous. A little 

 further search revealed the fact that the substance that pro- 

 duces the disease is barium. This is taken up by the plants in 

 the soil water, and is present in suflicient amount in many speci- 

 mens to cause "loco." Other plants grown in different regions 

 may not contain the poisonous substance. It is quite likely 

 that the obscure cause of "milk-sickness" may be discovered by 

 means similar to those which have identified the cause of 

 "loco." 



Number of American Ferns. — The number of fern 

 species in North America north of Mexico is pretty well- 

 known. At present it is set down at 218. There are also 86 

 species of Lycopodiums, Eqiiisetums, etc., which brings the 

 total number of fernworts in the region up to 300 or more. 

 This by no means represents the entire number of distinct 

 forms, however. The study of these latter has practically only 

 begun but already there is a list which numbers more than 200 

 and is steadily growing. These added to the true species make 

 considerably more than 500 species and forms in our region. 

 These have recently been listed with their geographical range 

 and abundance given in The Fern Bull tin. 



The Tubers of Nephrolepsis. — x^ny one who has 

 grown the sword fern (Nephrolepis cordifolia) for any length 

 of time must have noticed the potato-like objects to be found 

 on the underground parts of the plant. According to Prof. J. 

 W. Harshberger, these outgrowths are borne on underground 

 branches and are properly tubers. Most, if not all, the tubers 

 with which we are familiar are storehouses of food, but the 

 tubers of Nephrolepis are composed of thin-walled cells filled 

 with water and are therefore more in the nature of cisterns 



