446 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the day. The hornbeam contains less sugar and acid than the birch; 

 but the general results did not differ greatly. Incisions made at differ- 

 ent heights showed that the upper portion of the trunk contained about 

 twice as much nitrogen as the lower portion ; the greater part was in 

 the form of non-albuminoid nitrogonous substances. The hornbeam 

 contained less nitrogen than the birch. The proportion of mineral sub- 

 stances in tho birch steadily increased, the upper sap containing more 

 than the lower, and tho proportion being greater in the day than in tho 

 night. Tho upper sap contained more potassa, lime, and magnesia than 

 the lower ; there was only a very small quantity of iron, but a percep- 

 tible amount of manganese. Nearly all the sugar disappears before tho 

 hornbeam ceases to blossom, while it still appears in the birch until the 

 blossoming is completed. 



(3) Structure of Tissues. 



Endosperm.* — Prof. G. S. Boulger alludes to the ambiguity in the 

 use of the term endosperm. In Prof. Goebel's ' Outlines of Classification 

 and Special Morphology,' it appears with three, if not four, somewhat 

 disparate significations. To obviate this, the author proposes the term 

 "archisperm" for those structures formed before fertilization, or at an 

 early stage in the macrospore, viz. the meniscus-shaped " primary " 

 (female) prothallium above the diaphragm in Selaginella, the so-called 

 " endosperm " in Gymnosperms, and the antipodal cells of Angiosperms, 

 and either to reserve the term " endosperm " or to use " metasperm " for 

 those formed at a later stage, viz. the large-celled " secondary pro- 

 thallium " below the " diaphragm " in Selaginella, the " secondary endo- 

 sperm " in Gymnosperms, and the endosperm originally so called, formed 

 after fertilization by the division of the secondary nucleus of the embryo- 

 sac in Angiosperms. 



Formation of the Duramen. f — According to M. E. Mer, the heart- 

 wood or duramen is distingu shed from the wood of the peripheral 

 region (alburnum) by its being more deeply coloured, and by several 

 special industrial qualities. The duramen is often very apparent, as in 

 the oak, chestnut, &c, while in other trees this region is either indistinct, 

 or its dimensions are variable and its boundaries ill-defined. In some 

 cases the existence at all of heart-wood has been denied (as in the beech, 

 maple, fir-tree, &c), the wood of the centre and of the periphery pos- 

 sessing, for industrial purposes, almost identical qualities. But if a fresh 

 section be examined with care, the central portion will be found to 

 possess a deeper tint, especially if it be taken from near the base of the 

 tree. 



The author gives the following as the principal results of his 

 researches on the duramen. 



(1) The duramen does not differ from sap-wood either in structure 

 or in more advanced lignification, or in the existence of a colouring 

 matter, but only in the presence of a quantity of tannin or in some 

 cases of tannin and resin. 



(2) The characters which distinguish the heart-wood from the sap- 

 wood always exist, although the extent may vary. 



* Journ. of Bot., xxvi. (1888) pp. 37-9. 



t Bull. Soc. Bot. France, xxxiv. (1887) pp. 341-63. 



