ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 219 



Abies excelsa and Larix sihirica were partially dissolved by water or 

 glycerin, the parts of the cortex containing them being taken from 

 the stem in April. The sieve-plates of Equisetum are perforated by 

 " combining-bundles," which have not been found in true ferns. 



The author states that the callus-layers are usually to be found 

 only in the younger or. even the youngest parts of the cortex while still 

 in a state of vital activity, and considers it probable that the specific 

 function of sieve-tubes commences with the formation of callus, and 

 lasts only so long as this structure endures. 



Phyllomic Nectar Glands in Poplars.* — W. Trelease calls atten- 

 tion to the fact that these glands have been very generally overlooked, 

 and that they have been considered of little value by the systematic 

 botanist. He accounts for this by their being occasionally suppressed, 

 and by their limitation to the earlier-formed leaves. Still, most of 

 the American botanists refer to them, and Michaux figures them in 

 his monograph of the genus. In May 1880, Mr. Trelease's attention 

 was drawn by the action of some bees to examine the leaves of a 

 small aspen. The tree was covered with its newly expanded foliage, 

 and the bees were flying from leaf to leaf; they were seen to be 

 collecting nectar, which was poured out from a double gland at the 

 base of each leaf. These glands were placed on the upper sui-face 

 of the petiole at its union with the blade. On section and micro- 

 scopical examination, they showed the usual structure. They were 

 found not to occur on all leaves, but as a rule only on the first half- 

 dozen or less which appear on each branch in the early spring ; and 

 later on in the season, when these have fallen off, one may sometimes 

 examine all the leaves without detecting a single glanduliferous one, 

 and this on a species which produced them in abundance earlier in 

 the year. From an examination of the American species it would 

 seem that the greater number possess two or more distinct or con- 

 fluent glands, situated where the blade and petiole join ; and in those 

 few species where none were discovered it is quite possible that a 

 closer examination in the spring-time may show that they exist. 

 Thus on P. tremula, the weeping variety, a careful examination in 

 early May failed to show a single gland ; but a week or two later, 

 after several days' rain, the young branches grew very rapidly for 

 a short time, unfolding many new leaves, and the first three or four 

 of these on each branch bore large and active glands. The nectar is 

 greedily gathered by insects, chiefly Hymenoptera and Diptera. The 

 most numerous were the ants, who, as is usual in such cases, would 

 fight rather than give up a good position near a nectar-secreting 

 gland. The author regards these glands as protective. 



Histology of Urticacese.t — Karl von Demeter publishes (in 

 Magyar), an exhaustive account of the histology of Urticaceae, espe- 

 cially in relation to Boehmeria biloba, though reference is made also 

 to many other species. 



* Bot. Gazette, 1881. Cf. ' Nature,' xxv. (1882) pp. 327-8. 

 t K. von Demeter : ' Histology of Urticaceas, with special reference to Boeh- 

 meria biloba' (ill Magyar), Kkiusenburg, 1881, 13 pp., 2 pla. 



