854 REPORT— 1903. 



4. La fleuT des Gnetacies. By Professor LiGNiER. 



5. Parthenogenesis in Gnetum ula. By Dr. Lotsy. 



6. The Sandhill Vegetation of Birkdale, By Otto V. Darbishibe. 



The sandhills are formed by the wind blowing inland the sand, which is 

 supplied by the sea. 



Climatic conditions. — Rainfall of 31 inches ; plenty of sunlight and heat during 

 the day, rapid cooling during the night, heavy fall of dew; strong .sea winds 

 during the day, land winds at night, drying effect ; sand not raised much by the 

 wind. 



Edaphic conditions. — Sand not very salty ; loose grains, water soaks in and 

 evaporates rapidly; isolating surface layer of dry hot sand-reefs, interior mass 

 cool and moist ; water derived from rain and internal dew ; food material 

 present. 



Plant societies. — Shore dunes {Agropyrum, Psatnina) ; shore valleys {Hon- 

 kenya, &c.) ; inland dunes {Psamma) ; inland valleys on peat {Parnassia, &c.), 

 and on sand {Salix repens, &c.). Moving dune front encroaching on grassland. 



Common plant-features. — Rootstoclis; xerophil leaves (types of Psamma, 

 Honkenya, Salix, &c.) ; plants small ; trees reduced in size, in dune form ; plants 

 in tufts. 



Chief factors. — The sand and the wind. The plants are psammophytes, which 

 vary with exposure to wind. The sandhills are therefore an edaphic formation. 

 The dunes can be fixed by the binders, but temporarily only, till tlie supply of 

 sand from the sea is cut off. 



7. The Histology of the Sieve Tubes of Angiosperms. 

 By Arthur W. Hill, M.A. 



The paper deals with the structure and development of the sieve plate and of 

 the sieve fields, and also with the distribution and character of ' connecting threads ' 

 between the sieve tubes and the companion and cambiform cells in the phloem of 

 certain Angiosperms. The sieve plates of the mature sieve tubes, which occur 

 in the horizontal or oblique end walls of the tubes, are traversed by relatively 

 thick slime strings, each being inclosed in a callus rod. In the radial and tangen- 

 tial walls the slime strings, which are grouped into oval or rounded pitted areas, 

 are much smaller than those in the sieve plates, and some three to six strings are 

 inclosed in a callus rod. 



Connecting threads also occur between the sieve tubes and companion cells : 

 they are very short and numerous, and are usually situated in fairly deep and 

 transversely elongated pits. Between the sieve tubes and cambiform celk and 

 between the latter and the companion cells the small groups of threads are found 

 in small and deep pits. 



During the winter these various threads may be covered with callus, but only 

 on the sieve tube side. The development of the sieve fields is similar to that of 

 the sieves of Pinus, and the sieve plates, though differing somewhat in the details 

 of their development, agree in their essential features with the sieve fields. 



Groups of tine threads can be seen in the membranes of the pits in the lateral 

 walls of the youngest sieve tubes, which by the action of ferments (as it would 

 seem probable) are bored out and converted into slime strings, the cellulose 

 membrane in the immediate vicinity being at the same time converted into callus ; 

 and thus is formed the callus rod with its included slime strings. 



In the sieve plates the action of the ferment appears to proceed still further, 

 giving rise to a single large slime string in a callus rod. 



