246 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the leaves stand in a single dorsal row on the mature stem, while 

 younger plants and weaker lateral branches have their leaves in two 

 rows. The very complicated vascular-bundle system of the stem 

 consists of a number of anastomosing bundles which constitute, in the 

 mature plant, two concentric sheaths, from the outer of which spring 

 the root-bundles, from the inner the leaf-bundles. The bundle- 

 system of weaker shoots is a simpler form of the same structure. In 

 Polypodium tceniosum the leaves are arranged in several dorsal rows, 

 with more or less evident parastichies. 



In all the Polypodiace^e examined, those with the leaves in a 

 single [row, like P. tceniosum, as well as in many with the leaves in 

 two dorsal rows, P. vulgare, aureum, Phymatodes, ireoides, &c., the 

 leaves originate in the growing point in the same arrangement as 

 they exhibit when mature ; and no displacement takes place, as is 

 sometimes described. 



North American Isoetes.* — G. Engelmann describes in detail 

 the North American species of Isoetes. Only one species, I. cuhana, 

 belongs to the section with three-lobed stem ; all the rest, including 

 one new species, /. Howellii, have the stem two-lobed, like our 

 I. lacustris. These he divides into three sections : — (1) Submerged 

 species, with tetragonous leaves, almost always without stomata ; 

 without peripheral sclerenchymatous bundle; velum more or less 

 imperfect. (2) Amphibious species, with tetragonous leaves and 

 numerous stomata. (3) Terrestrial species, with numerous stomata, 

 and peripheral sclerenchymatous bundles in the nearly trigonous 

 leaves. 



Fungi. 



Spermogonia of TJredinese and their Relation to Insects-f — 

 E. Eathay has examined the structure of the spermogonia of a number 

 of Uredineee, in relation to the visits paid to them by insects, attracted 

 by their bright colour, sweet taste, and frequent odour. In all the 

 21 species examined, the spermogonia, whether tasteless or more or 

 less intensely sweet, were found to contain a sugar capable of reducing 

 Fehling's solution, believed by the author to be arabinose. In 

 14 kinds he made direct observation that the contents of the emptied 

 spermogonia attract insects, of which as many as 135 distinct species 

 were seen to visit them. 



The spermogonia excrete the saccharine fluid not only during 

 rain, but even when the air is dry ; this Eathay considers to be 

 effected, as in the nectaries of flowering plants, by osmotic action ; the 

 gelatinous fluid carrying the spermatia with it. As long as the 

 nature of the spermatia is not fully understood, the object of this 

 contrivance for attracting insects must remain unexplained; the 

 author believes them to be sexual organs with a male function. 



* Trans. St. Louis Acad. Sci., iv. (1882) pp. 358-90. Sec Bot. Centralbl., 

 xii. (1882) p. 290. 



t Denkschrift der K. Akad. Wiss. Wien, xlvi. (1882). Sec Bot. Ztg., xl. 

 (1882) p. 906. 



