119 



coagulable ingredients without becoming rigid, and finally the 

 protoplasm and mucilage disappear also. The plates always oblit- 

 erate by the thickening of the callus layer and the narrowing of 

 the pores. The effect of the latter change is that the mucilage 

 lining the pores is changed into massive threads {Cuciirbita) which 

 become thinner and thinner until they disappear, being most likely 

 transformed into callus. When the obliterating sieve-tubes are 

 injured no accumulation of mucilage at the plates can be formed, 

 because the mucilage contained in them is not fluid but rigid like 

 caoutchouc. 



The sieve-tubes are in direct communication with one another 

 and with their accompanying cells by means of delicate threads ; 

 notj however, with the cambiform cells, which, in their turn, are 

 connected by threads of protoplasm. J. S, 



Observations on Diatomace<£ from the Neighborhood of Hert- 

 ford. — Isaac Robinson. (Trans. Hertfordshire Nat. Hist. Society, 

 vol. iv., part 7.) 



The writer alludes to the faci that after a heavy rain the 

 coloring matter of rivers often consists largely of diatoms. He also 

 records his observations of cysts containing young diatoms in 

 various stages of development. Appended is a Hst of 154 species 

 found in Hertfordshire, mostly in the vicinity of Hertford. 



C. H. K. 



Botanical NoteSi 



Botanical Section of the Biological Society of Washington. 

 We have received a brief abstract of the papers delivered at the 

 first meeting, from the Secretary. Prof. Burgess spoke on the 

 Fresh-water Algae, reviewed the literature of the subject, and 

 called special attention to the work of American botanists. Prof 

 F- H. Knowlton followed with some remarks on '' A Case of 

 Sewer Obstruction by the Roots of Trees." Prof S. M. Tracy 

 described some Fungi from the Arid Regions, collected during a 

 recent trip, including twenty-five species of Erysiphe. Several 

 new Pucciinas and jEcidiums were also collected. Miss E. A. 

 Southworth read a paper on the Gleosporium of the Wax Bean 

 {G, Lindermithiamim), as a result of some studies carried on 

 under the direction of Prof. F. L. Scribnen 



