394 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the lateral walls, the number of terminal plates decreases until there is 

 only one terminal plate with relatively large meshes, and the lateral 

 plates become " sieve-fields " or lattices. Palseobotany, ontogeny, and 

 studies of xylem have induced many botanists to believe that herbaceous 

 plants are more advanced in their evolutionary development than woody 

 plants. This study of the sieve-tube adds another argument in favour 

 of this view. 



Comparative Anatomy of Dune Plants.*— Anna M. Starr has 

 made an extended study of the plants of the Indiana dunes, and sum- 

 marizes the following conclusions. 



Conditions in the dunes are severe for plant-life, including direct 

 illumination and reflection, extremes of temperature, strong winds, 

 sand-blast, and sandy soil, the result of all these factors being increased 

 evaporation. The presence of considerable water above the water-table 

 makes conditions less severe than they otherwise would be. The 

 response to these conditions by true dune plants is seen in the pre- 

 dominance of low vegetation, long roots, woody stems, thick leaves 

 (which may be reduced, equilateral, evergreen, or folded), succulence, 

 hairs, thickened epidermis and cuticle, deep palisade, sunken stomata, 

 and well developed mechanical and conductive tissues in all parts. 



Plants generally growing in mesophytic situations, when found also 

 on the dunes, show the following modifications : (a) in the leaf — increased 

 thickness, decrease in depth and increase in surface-extent of epidermal 

 cells, increase in thickness of the outer wall of the epidermis and of the 

 cuticle accompanied by ridging, increase in palisade, in hairs, in con- 

 ductive and mechanical tissues ; {b) in the stem — decrease in the length 

 of internodes, increase in the number of vessels and in the area of their 

 cross-sections, giving greater conductive space, increase in thickness of 

 the walls of vessels and of the fibres accompanied by decrease in lumen 

 of fibres, giving more wood, increase in the number of growth-rings in 

 stems of a given size, showing slowness of growth, increase in mechanical 

 tissues outside the wood, and increase in cork. 



Reproductive. 



Development of Microsporangia and Microspores of Abutilon 

 Theophrasti.t— V. Lantis finds that Abutilon Theophrastl shows the 

 single row of archesporial cells that has been reported for the other two 

 investigated species of Malvaceae, and in the formation of primary 

 parietal and primary sporogenous layers there is also great similarity. 

 In Abutilon, however, each primary sporogenous cell produces four 

 mother-cells, while in the other Malvaceae studied only one is formed. 

 The mother-cell stage in Abutilon persists until three parietal layers, 

 the inner being a well developed tapetum, are fully formed, after which 

 the characteristic heterotypic and homotypic divisions take place 

 rapidly. This period of tetrad formation is marked by a multiplication 

 of nuclei in the tapetal cells. The arrangement of the microspores in 

 the tetrad is tetraliedral and very regular. Tlie tapetum continues to 



* Bot. Gaz., Iv. (1913) pp. 265-305 (35 figs, in text), 

 t Bot. Gaz., liv. (1912) pp. 330-5 (text figs.). 



