592 SUMMARY OF CURRENT RESEARCHES RELATING TO 



behaviour towards chemical reagents they appear to be identical with 

 chondriosomes, and the author regards this conception as a fact of con- 

 siderable importance. 



Structure and Development. 

 Vegetative. 



Vegetative Bud of Cordaites.* — 0. Lignier has studied the struc- 

 ture of a vegetative bud of Cordaites lingulatus, discovered in the 

 siliceous strata of Grand' Croix. The bud is much elongated, resembling 

 that of grasses, and the length of the present specimen, i.e. :3 cm., is 

 considerably less than the total length. It consists of four spatulate 

 leaves, overlapping one another but witliout imbrication. Both the 

 inner and outer leaves have chlorophyll-tissue, but only the outer ones 

 have a definite palisade and spongy layer. In the fibro-vascular strands 

 the phloem differentiates before the xylem, but development never 

 proceeds far. Xylem-formation is at first centripetal, and the most 

 slender tracheids are nearly at the centre of the procambial strand, 

 but subsequent development is centrifugal ; the centripetal wood con- 

 sists of a few tracheids, and spiral, scalariform, and pitted vessels ; the 

 centrifugal arc consists of narrow tubes, which may be pitted. There 

 are no secondary vascular tissues. The cortex consists of several layers, 

 and thickening begins early, extending outwards towards the epidermis 

 and inwards towards the vascular strands; the cell-walls are often 

 pitted. The two glandular strands accompanying each vascular bundle 

 appear to belong to the cortex, and may have secreted gum. The veins 

 are dichotomous, the splitting starting at the lower surface Many of 

 the cells of the lower epidermis are prolonged into hairs. C lingulatus 

 resembles G. principalis in its reduced stereome structure, but is more 

 like C.filicis in the structure of its bundles and cortex. 



Cambium-development in American Larch.f — L. Knudson has 

 studied the development of the cambium of Larix laricina. Investiga- 

 tions were first conducted in 1909, and the trunks of four trees of 

 equal age were kept under observation. It was found that the cambium 

 began to increase in diameter about April 19, and an increase in 

 the phloem became evident in the middle parts of the trunk. On 

 May 25 both phloem and cambium had increased over the entire trunk, 

 but the greatest increase was in the middle region. The greatest 

 increase in the phloem took place during the next few weeks and 

 coincided with the time of the greatest increase in the xylem. Little 

 or no xylem was formed before the end of May, but development was 

 complete by the middle of July. 



In 1911 the branches of a single tree were studied, and it was found 

 that the increase in diameter begins in the middle lateral branches, 

 subsequently extending to the basal and apical branches. In individual 

 branches growth begins at the apex and extends to the base. The 

 increase in the diameter of the trunk precedes that of the branches. 



* Ann. Sci. Nat., xvii. (1913) pp. 233-54 (18 figs.). 



t Bull. Torrey Bot. Club, xl. (1913) pp. 271-93 (2 pis.). 



