602 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Structure and Development, 

 Vegretative. 



Red Wood in Conifers.* — J. White has carried out a number of 

 experiments upon Conifers in order to test the truth of the suggestion 

 that the formation of red wood is " a morphogenic response to a gravi- 

 bational stimulus." The plants used were grown in pots and rotated 

 on a klinostat, and the results show that, while the formation of red 

 wood is due to the stimulus of gravity, the thickness of its tracheids 

 appears to be the result of a light-stimulus ; the tracheid walls of 

 strougly illuminated branches were always thicker than those under a 

 less intense illumination. Under similar conditions, the walls of the 

 tracheids of both red and white wood were of equal thickness. It is 

 improbable that pressure and tension produced by forcibly curving the 

 branches has any effect upon the thickness of the tracheids of either 

 white or red wood, or upon the formation of red wood. The minimum 

 time for response to the stimulus of gravity in the production of red 

 wood is 2 hours. 



Embryology in the Palmaceas, Musaceae, and Cannaceae.t — C. L. 

 Gatin contributes a note upon his recent studies of the anatomy and 

 development of the embryo in the Palniaceas, Musaceae, and Cannaceae. 

 The embryos have several points in common, of which the following 

 are the most important. They are all surrounded by an epidermis which 

 is discontinuous opposite the radicle, where it gives place to irregular 

 cells representing the remains of the suspensor. The central cylinder 

 of the radicle is well-defined from the first, but its cortex and cap 

 differ greatly in their degree of differentiation. In all cases the radicle 

 is endogenous, being most markedly so in Pinanga and Calamus, which, 

 in this respect, resemble the Grasses. There are two phases of develop- 

 ment in germination : (1) the phase of preparation, (2) the phase of 

 germination proper ; in the former the seedling issues from the seed, 

 while in the latter the various organs complete their development. 

 In Palms the growth of the cotyledon is very great, but the shape is 

 determined by the interior of the seed ; in Cannaceas and Musacea? the 

 growth is less, but the form more, primitive. As stated previously, 

 when the plumule and radicle are in the same straight line, no ligule 

 is formed, while if the angle between the radicle and plumule is less than 

 180°, a ligule is present. 



Hibernation and Vegetative Reproduction of Stellaria.i — T. 

 Holm has studied American species of Stellar/)/, and distinguishes 

 three types of vegetative reproduction. The first type, represented 

 by S. p ahcra, has no rhizome, but persisting aerial stolons. There are 

 two kinds of shoots : floral, which die down when the fruit is mature, 

 and vegetative, which arise as horizontal branches, and form new 

 individuals. As soon as these vegetative shoots have formed roots, 

 the internodes break down and produce separate plants, which hibernate 



* Proc. Roy. Soc. Victoria (n.s.) xx. 2 (1908) pp. 107-24. 



t Comptes'Reudus, cxlvi. (1908) pp. 93S-10. 



\ Amer. Journ. Sci., xxv. (1908) pp. 315-22 (G figs.). 



