370 SUMJIARY OF CURRENT RESEARCHES RELATING TO 



There are often found cells and tissues wliich serve purposes of 

 local assimilation, as glandular and stinging hairs, the guard-cells of 

 stomata, &c. 



The origin of the assimilating tissue varies greatly. It may 

 arise from the cambium, the fundamental parenchyma, or the young 

 epidermis. 



Tlie fundamental parenchyma of the stem passes without inter- 

 ruption into the parenchyma of the leaf-stalk, which is itself in con- 

 nection with the parenchymatous sheaths of the vascular bundles of 

 the leaf; this entire system forming the priucij)al channel for the 

 passage of the jiroducts of assimilation. 



In addition to its jirimary function, the assimilating system of 

 many evergreen leaves, as those of conifers, fulfils a secondary func- 

 tion, viz. the storing up of the products of assimilation during the 

 period of repose. 



Fibrovascular Bundles of Monocotyledons.* — The fibrovascular 

 bundles of Monocotyledons are normally of two kinds, collateral, in 

 which the xylem and phloem run side by side, and concentric, in 

 which a ring of xylem, usually closed on all sides, encloses a central 

 mass of phloem. L. Kny points out that not a few monocotyledons 

 possess fibrovascular bundles which do not corresjiond to either of 

 these types. Not unfrequently two or more groups of soft bast are 

 separated by masses of sclerenchyma. In a number of palms bipar- 

 tition of the phloem occurs, and in Wiapis fldbeUiformis tripartition is 

 the rule. Sclerenchyma frequently forces its way from both sides 

 between the phloem and xylem, separating them from one another. In 

 Tesfudinaria and other Dioscoreacefe the separation of the phloem 

 into two distinct groujis is especially marked. The object both of 

 this separation and of the interposition of sclerenchyma, the author 

 believes to be the mechanical strength gained thereby. 



Sieve-Tubes.f — E. Janczewski continues his researches | on the 

 sieve-tubes of Dicotyledons, with especial reference to Aristolochia 

 SipJw, Tilia parvifolia, and Vitis vinifera. 



They may be formed out of cambium-cells in two different ways : 

 — (1) The cambium-cell, after detaching derivative cells on each 

 side, developes the sieve-tube-cell directly ; and the sieve-tubes are 

 then arranged in radial rows, in contact with one another by their 

 tangential walls ; or (2) the cambium-cell divides longitudinally and 

 tangcntially into two cells of unequal size, of which the outer and 

 larger one becomes the sieve-tube-cell either immediately or after 

 the separation of lateral derivative cells, while the inner and smaller 

 cell breaks up, by transverse division, into a row of parenchymatous 

 cells. In this latter case they are separated from one another, and can 

 touch one another only by their radial walls. A single cambium-cell 



* Verhandl. hot. Ver. Prov. Brandenburg, xxii. (1881) pp. 94-109. See Bot. 

 Ceiitralbl., ix. (1882) p. 79. 



t SB, Akad. Wiss. Kiaksiu, ix. (1881) (5 pis.). See Bot. Centralbl, ix. (1882) 

 p. 15. 



X Sue lliis Journal, iii. (1880) p. 824. 



