The Optical Quality of Mr. Tolles' i Objective. 13 



4-8 inches high, pale rufous red ; the cortical cells non-porose, in 

 three strata, the icoody zone red. Cauline leaves precisely like 

 those of ;S^. squarrosum. Hamuli distant, 4-5 in a fascicle, 2-3 

 divergent, terete ; the leaves imbricated throughout, and only 

 having the apices slightly recurved ; broadly ovate, pointed, three 

 toothed, in structure agreeing with those of 8. squarrosum. Cor- 

 tical cells of branches in a single stratum. 



Male amentida elongated, broivnish, fertile and thichened in 

 the lower part, and beyond this extended into a slender sterile 

 branch ; the bracts broadly ovato-lanceolate, pointed, agreeing in 

 structure uith the branch leaves. 



Fruit seated in the coma, or in the upjoer fascicles ; the bracts 

 resembling those of 8. squarroswn. 



Hab. — About the edges of bogs and springs in subalpine dis- 

 tricts ; sparingly distributed. In this country it has been found 

 by Mr. Wilson at Knutsford Moor, Wybunbury Bog and New- 

 church Bog in Cheshire ; by McKinlay at Domie ; and by 

 Mr. Stabler at Btaveley, Westmoreland. 



This plant has usually been regarded as a variety of 8. squar- 

 rosum, and Professor Lindberg has recently expressed to me his 

 coincidence with this view ; structurally there is absolutely no 

 distinction between them, but in external aspect 8. teres closely 

 resembles 8. strict um. The beautiful and instructive specimens 

 collected by Limj^richt at Bunzlau, and distributed under No. 1153 

 of Kabenhorst's Bryotheca, combine the characters of both, the 

 upper part having the imbricated leaves of 8. teres, the lower part 

 the squarrose leaves of typical 8. squarrosum. There is thus left 

 to us only the dioicous position of the inflorescence, and the slight 

 difference in the male amentula. 



III. — Tlie Optical Quality of Mr. Tolles' ^ Objective. 

 By Egbert B. Tolles. 



Further but brief discussion of the well-whipped subject of 

 angular aperture is here offered on my part, being again sum- 

 moned to the front after repeated dismissals by Mr. Wenham, while 

 he imparts " further information " as to optical law concerned. I 



EXPLANATION OF FIGURES. 



Fig. 1. — m, Front surface of middle. 



R, R, Outside rays of pencil from middle 60°. 

 R' R', Pencil traced from Focus of 82°. 

 Outside pencil at Focus of 90°. 

 „ 2. — Angle reduced by cIosukj the lenses. 



