OR HAY-FEVER. 175 



Rag-weed, Ambrosia arUmiskefolia, T,., and the Golden-rods, 

 Solidai^-o allissima, L., ^. laiiccolafa, L., and S. sqiiarrosa, Mulil., 

 which three forms are typical. I have here also, under these 

 microscopes, pollen of all these plants, mounted on slides ; also 

 here are enlarged drawings of the pollens. 



Fresh Rag-weed pollen is very nearly spherical. The granule 

 measures in these specimens, which are a little distorted by long 

 drying, ^^^ inch in length by ^^ inch in width. In a fresh speci- 

 men, or such as floats in the summer air, so fine are the points of 

 the spines that they are to that of a cambric needle as it is to the 

 point of a marling-spike, or even a crowbar. And yet this object, 

 with its subtle armature, is literally invisible to the unaided sight. 

 See Plate XV., Fig. i. 



The pollen-grains of the Golden-rods are sub-elliptical, both 

 ends being of the same size. They are very spiny, and the spines 

 are relatively longer than those on the pollen of the Rag-weed. 

 They are of two lengths on the same granule. The pollen of S. 

 altissima, the most abundant, in these parts, of the many species, 

 is in length -— inch, and in width j-^^,, inch. The flowers are in a 

 recurved panicle, not unlike the graceful spray of an ostrich plume. 



An abundant species is the S. laiiccolafa, whose flowers are 

 borne in scattered corymbs, or flattish-topped clusters, something 

 in the manner of the Wild Carrot, which habit is in striking con- 

 trast with the Golden-rods generally. This pollen makes a 

 narrower ellipse than the one just mentioned, the two diameters 

 being ^ and ^ inch respectively. 



S. sqiiarrosa is less common than the other two species. The 

 flowers are more conspicuous, and arranged in a showy wand, or 

 sceptre-like spike. Its pollen measures ^ by j^^ inch, hence it 

 is larger than that of S. altissima. 



And exceedingly interesting is the end view, since it shows a 

 tripartite disposition, being as it were depressed at three points. 

 Now these depressions are simply the terminations of three longi- 

 tudinal canals on the sides. The end view is shown in Fig. 2 ; 

 and Fig. 3 shows one of the longitudinal grooyes. I find these 

 marks much fainter in S. altissima^ and barely discernable in S. 

 lanceolata. 



