THE ROOT-HAIRS, CAP, AND SHEATH OF AZOLLA. 



R. G. Leavitt. 



(with plate XVI ) 



Roots spring from the prostrate floating shoots of Azolla in 

 acropetal succession at the points of branching. They are from 

 2 to g'^™ in length, undivided, slender, and delicate, and in 

 A, filiadoides and A. carolmiana are often, perhaps generally, 

 provided with long outstanding hairs. These trichomes are 

 peculiar in that they originate in the immediate neighborhood 

 of the growing point, and from the first are marked out as cells 

 designed for a distinct office. The way in which the hair initials, l 



or fundaments of the root-hairs, are cut off, and the specialized 

 character of the mature structures have not been described, so 



far as I am able to learn/ 



// 



which Strasburger chiefly founded his classical memoir, '*Ueber 

 Azolla," presented a condition of the root quite unlijce that 

 which I have found in the same species. His plants had the 

 roots enveloped in root-sheaths, and must have been entirely 

 destitute of the trichome structures which form the principal 

 subject of the present account. My own plants were somewhat 

 variable, the roots occasionally being devoid of hairs- Yet the 

 three lots of living material from independent sources which I 

 have been able to see all exhibit the interesting process of hair 

 formation to be described. 



THE SHEATH AND CAP, 



;j 



+ 



As the root-sheath and cap in the plants studied do not 



* 



entirely conform to Strasburger's account, I shall take occasion 

 to note the points of difference. For the sake of completeness 

 Strasburger's exposition of the origin and early stages of the 



^Several references to the existence of these trichomes and one account of 

 their peculiar distribution are to be found: Westermaier and Ambronn, Ueb6r 

 eine biologische Eigenthumlichkeit der Azolla caroliniana. Verhandl. Bot. Verein. | 



Provinz Brandenburg 22: 58. 1880; Berggren, S., Om AzoUa's prothallium och 

 embryo. Lunds Univers. Arsskrift 16: 1878-1879. 



I 



414 [DECEMBER 



