Pollard: The Genus Achillea in North America 3G7 



be reduced to the aggregate A. MillcfoUnin bybotanists of con- 

 servative tendencies ; but it is difficult to comprehend why A, 

 borcalis, which belongs to Ptannica and was placed there by De 

 Candolle should have been transferred to the other division of the 

 genus and combined with the type species thereof. 



The great mass of our Ariierican yarrows may be regarded as 

 belonging to two species. Those of the East seem to be referable 

 to the true European A. MillcfoliiDU^ having the same inflores- 

 cence, the same rather diminutiv^e rays and mucli dissected glabrate 

 foliage. In the Rocky Mountain region there is apparently a 

 commingling and an intergradation with A. Immlosa, w^hich al- 

 though extremely polymorphous, is usually distinguished by its 

 much larger rays and more or less lanate pubescence. I have made 

 a careful dissection of the heads of thirty specimens from widely 

 separated localities in the West, and while there are often differences 

 in the involucral bracts, the measurement of the rays and the ap- 

 pearance of the foliage, these differences cannot be correlated. I 

 am therefore convhiced that in the present state of our knowledge 

 it is better to leave the species as an aggregate which we may per- 

 haps regard as already in a process of differentiation. Future 

 collections and observations, particularly with respect to altitudinal 

 distribution, will undoubtedly enable us to make a more satisfac- 

 tory disposal of these forms. 



Specimens of ^t'/;//A'(^ having pink or even rose-red rays are 

 not uncommon, particularly east of the IMississippi. One of these 

 was described by Ventenat, under the name of.-^. asplcnifolia^ from 

 a e^arden-grown indiv^idual, the seeds of which were brought from 



Carolina by IBosc ; but De Candolle observes that the plant had 

 been well known in European gardens long before Bosc's time. 

 My first impression was that Ventenat's description applied only to 

 the ordinary pink-rayed form of A, Milkfoliuni ; but having ex- 

 amined his illustration in connection with some very interesting 



L 



herbarium material. I am now convinced that A. a 



spli 



cultivated plant only, the origin of which is uncertain. The shape 

 and position of the leaf-segments is entirely different from any form 

 of Millcfolhim^ and the only specimens matching figure and descrip- 

 tion that have come within my observation were from cultivated 

 indi\'iduals. All wild yarrows with red or pink rays will be found 



