6G2 SUMMARY OF CURRENT RESEARCHES RELATING TO 



much as it possesses two separate membranes, one containing the 

 eoarso and the other tho fino areolations. The outer is a strong, 

 coarsely-marked structure, the areolations being for the most part 

 circular or oval in outline. The intervening silex is granulated on 

 the exterior, and has a brownish colour by transmitted light. With 

 reflected light, however, it appears white and sparkling, not unlike 

 loaf-sugar. The interior membrane is very transparent and covered 

 with minute perforations (only lately discovered, and which have 

 been called tertiary markings). But in addition to these are what 

 have long been known as the secondary markings, viz. white bright 

 spots, which are arranged in rows radiating from the centre. Theso 

 secondary markings must not, tho authors consider, be regarded as 

 perforations, as they have not found an instance of a fracture passing 

 through them. 



Another figure shows the secondary and tertiary markings on the 

 interior membrane, as seen through the coarse areolations of the 

 exterior membrane. The best way of examining the secondary mark- 

 ings is to use a 1/2 or 4/10 objective, with a lieberktihn, the specimen 

 mounted dry, with the concave side uppermost. The tertiary are 

 more difficult to sec, and will require a higher power. 



The fracture passing through the perforations in a valve of Pleuro- 

 sigma angulatum is also shown. This diatom has but one membrane, 

 and only one kind of perforations. To show this properly a lens 

 must be very well corrected, and have its glasses very perfectly 

 centered. 



Lichenes. 



Gonidia of Lichens.* — Dr. K. B. Forsell replies to Zukal's 

 strictures in his ' Flechtenstudien ' f on the author's views on the 

 nature of the connection between the algal and fungal elements in 

 lichens, and defends his statement in his work on the Glceolichens, \ 

 that Zukal has in many cases assumed, without sufficient evidence, a 

 genetic connection between algre and gonidia, and has hence been led 

 to incorrect conclusions. 



Fungi. 



Symbiosis in the Vegetable Kingdom.§ — Prof. B. Hartig confirms 

 the account given by Frank, || of the occurrence of niycorhiza 

 (Bosellinia quercina) on the roots of the oak. He considers, however, 

 Frank's statement that many Cupuliferaa depend entirely on the 

 mycelium of fungi for their nourishment as too absolute. It is not 

 unfrequently entirely wanting ; and, especially at the period when the 

 trees are taking up the largest quantity of water and nutrient sub- 

 stances, the newly formed apices of the roots are entirely free from the 

 fungus, which attacks them only in autumn and winter. 



* Flora, lxix. (1886) pp. 49-64. 



t See this Journal, ante, p. 112. J Ibid., ante, p. 485. 



§ SB. Bot. Verein Miincken, Nov. 11, 1885. See Bot. Centralbl., xxv. (1886) 

 p. 350. || See this Journal, v. (1885) p. 844. 



