406 SUMMARY OF CURRENT RESEARCHES RELATING TO 



The author describes some experiments with Liquidamhar ; and the 

 result may be summed up by stating that the tendency is for the 

 summer growth to form ligneous walls, the plate-cells always cork. 

 In Quercus the results were very similar, and the same may be said of 

 Acer campestre. In Acer monspessulanum the results were the same, 

 excepting that there were ligneous cells along the line of breakage. 

 Euonymus alatus differed from the preceding only in that the tendency 

 to ligneous cells in the summer growth was more marked. In the 

 formation of the wings of Quercus and Acer, and others of a similar 

 type, the first steps in the process are easily explained on the score of 

 purely physical causes. The breaking of the tissues is the result of a 

 strain greater here than in other places on the fresh yielding tissues. 

 The author then says a few words on the function of lenticels. 



Various facts in regard to the anatomy of these growths have sug- 

 gested certain inferences. The most important of these are : — (1) Young 

 stems, which are entirely encircled by cork-wings, are found to lack 

 other means of communication with the outside air. The anatomy of 

 the wing in these cases is such as to enable it to supply this deficiency 

 and to act as lenticels. (2) The wings of the horizontal branches of 

 Liquidambar, covering as they do only part of the circumference, perform 

 in part the same function ; at the same time they increase the surface 

 sufficiently to allow the growth within, while the remaining part of the 

 surface of the stem retains the character and office of the early periderm. 

 (3) In Euonymus, the symmetry of the stem is preserved, the surface is 

 enlarged by the wing, while all the remaining surface of the stem plays 

 the part of assimilation. (4) The characteristics of autumn cork are 

 exactly those of autumn wood, the tracheal element alone excepted. 

 Could it be proved that these changes are due to the same cause, another 

 means of deciding the question as to the cause of the autumnal growth 

 of wood, or annual rings, would be obtained. 



Researches on the Periderm.* — M. H. Douliot now describes the 

 periderm of the Hypericaceae. M. Vesque found a considerable differ- 

 ence in structure to exist between Hypericum and Ancistrolobus pulcJiellus ; 

 the author, however, states that there is no difference in the origin of 

 the periderm. In the nine genera of true Hypericacese belonging 

 to the two tribes Hypericese and Vismiese, the periderm is pericyclic. 

 Franhenia differs from the true Hypericacege in the two alternate whorls 

 of stamens, and also in the origin of the periderm, which is not pericyclic 

 but hypodermal. The author concludes by some observations on the 

 development of cork in the Hypericaceae. In Hypericum calycinum a 

 folded layer may be observed in the middle of the soft cork, a phe- 

 nomenon which has already been noticed by Sanio in a species of 

 Melaleuca, and which is frequent in Kosaceas, CEnothereas, and Myrtaceae. 

 In Cratoxylon coccineum the periderm possesses folded layers and layers 

 of hard cork with thickening cells in the form of a U, the opening being 

 turned inwards. This form of thickening is also met with in the cells 

 of the endoderm. 



(4) Structure of Organs. 



Pollen of the ConvolvulacesB.t— Dr. A. C. Stokes describes the 

 minute structure of the pollen of several species of this order, especially 



* Morot's Journ. de Bot., iii. (1889) pp. 37-9. Cf. this Journal, 1888, p. 987. 

 t The Microscope, ix. (1889) pp. 33-43 (1 pi.). 



