-iS— 



Isoctcs Orcuttii A. A. Eaton. Growing in the same evanescent 

 pools at San Diego, already mentioned as the habitat of Pilu- 

 laria Americana. Like it, they soon disappear after the pools 

 dry up, and occur at all only in wet winters. San Diego is 

 the type station, and the plant has been collected only there and 

 in adjacent Lower California. 



THE MEASUREMENT OF VARIATION IN EQUISETUM. 



By Wizard N. Cujte. 



Two years ago, I had the pleasure of collecting in Louisiana, 

 that form of the scouring rush called Equisctum robustum. It is 

 the only species known to grow in that State and has always been 

 identified as true robustum from the time of Rafinesque to the 

 present, but upon studying it, I could see no differences worthy 

 of note between it and the common Equisctum hyemale of the 

 Eastern States. I was, therefore, not surprised when Mr. A. A. 

 Eaton named it a mere variety of E. hyemale. Opinions as to 

 what are specific differences, however, are likely to vary and with 

 the idea of trying to find a safe basis for an estimation of value 

 of these differences I decided to see what a measurement of the 

 various parts would show. 



MATERIAL. 



Through the kindness of Prof. R. S. Cocks, of New Orleans, 

 I received upwards of 100 specimens of E. robustum from that 

 city, while Mr. H. C. Skeels furnished me with a similar number 

 of stems of E. Jiyemale from Joliet, 111. I also collected about a 

 hundred specimens of hyemale at Patterson, 111. The material 

 was selected by going to an Equisctum thicket late in the year 

 after all growth had ceased and selecting the nearest stems with- 

 out regard to height or thickness, cutting them close to the earth. 

 From this material all defective stems were subsequently re- 

 moved ; defective stems being defined as those that plainly had 

 not matured, those that had been injured, and stems of the second 

 year bearing branches. Mr. Skeels' specimens were. selected with 

 the view of getting a complete series of stems from small to large 

 regardless of the part of the thicket from which they came. This 

 will account for certain discrepancies in the measurements of the 



