264 SUMMARY OF CURRENT RESEARCHES RELATING TO 



many leaves ; the apices of the papillae have the effect of bright points on 

 a dark ground, the light being reflected from them in one direction only, 

 while their lateral surfaces scatter the light. 



While albinism is the result of degeneracy, Dr. Hassack regards a 

 red colour as a direct consequence of light, and as a contrivance to protect 

 leaves from the destructive action of too strong light on the chlorophyll, 

 and too strong respiration ; it is hence found especially in young leaves, 

 or in the leaves of those plants which grow in very high altitudes, or in 

 very cold latitudes. 



Relationship of the Anatomical Structure of Leaves to their Origin.* 

 — M. L. Dufour states that, in those leaves in which the normally upper 

 and under surfaces become reversed in the course of growth, either the 

 anatomical characters of the two surfaces become completely changed with 

 their relative position, or some of the original differences remain unchanged. 

 The former is the case with Alstroemeria psittacina and Allium ursinum, the 

 latter with Allium nutans and other species, Eustrephus angustifolius, and a 

 large number of grasses. The fibrovascular bundles never undergo any 

 change of position or of structure with the reversal of the position of the 

 leaves ; the characters most liable to change are the distribution of the 

 stomata, the position of the palisade-parenchyma, and the relative degree of 

 hairiness. 



Petiole as a Taxonomic Organ.f — According to M. L. Petit, a trans- 

 verse section of the terminal portion of the petiole may, within certain 

 limits, be used for the purpose of determining the natural order to which 

 a plant belongs. The following are the principal variations in its cha- 

 racters : — A. The transverse section exhibits secreting canals ; a, a certain 

 number of these canals are arranged regularly behind the peripheral 

 bundles ; (1) no crystals, bundles isolated, near the epidermis (Umbel- 

 liferae) ; (2) usually macles, bundles isolated or united into a ring, near the 

 centre (Araliacete ; Hydrocotijle is intermediate between these two) ; h, 

 secreting canals arranged irregularly ; (1) macles, bundles united into a 

 ring (some Malvaceae); (2) no macles, bundles distinct (some Compositae). 

 B. The transverse section exhibits no secreting canals ; a, bundles bicol- 

 lateral ; (1) median bimdle well developed; a, laticiferous tubes (Asclepi- 

 adeae, Apocynaceae) ; /8, laticiferous cells arranged in rows (Convolvulaceae) ; 

 y, no laticifers, crystalline granulations (Solanaceae) ; 8, no laticifers, 

 macles (Myrtaceae) ; (2) bundles nearly equal, no crystals ; 6, no bi- 

 collateral bundles ; (1) macles, under this class are included a large number 

 of minor variations ; (2) no macles, a, numerous crystalline granulations in 

 the same cell (some Chenopodiaceae) ; /3, crystals solitary (some Legumi- 

 nosae) ; y, no crystals (to this class again belong a number of varieties, 

 distinguished by smaller differences). 



The author suggests that these characters may be useful in assisting to 

 determine the position of fossil plants. 



Structure and Physiology of Stomata. | — Dr. H. Leitgeb has tried the 

 experiment of separating the guard-cells of stomata from the adjacent 

 epidermal cells and subjecting them to the action of stimuli, to which he 

 found them very sensitive, and capable also of preserving their vitality for 

 an extraordinarily long period. The experiments were made chiefly on the 

 epidermis of the perianth-leaves of Galtonia candicans, in which the 

 posterior wall of each guard-cell is connected with the opposite wall of the 



* Bull. Soc. Bot. France, viii. (1886) pp. 268-75. 



t Comptes Rendus, ciii. (1886) pp. 767-9. 



X MT. Bot. Inst. Graz, i. (1886) pp. 123-84 (1 pi.). 



