484 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Osmanthus Delavayi (Bot. Mag. tab. 8459).— China. Family 



Olcaceae, tribe Oleineae. Shrub, 8 feet high, evergreen. Leaves 

 I inch long, coriaceous. Flowers in terminal clusters, white. Fragrant. 



G. H. 



Palms, On the Growth in Thickness in. By J. C. Schoute 

 (Ann. Jard. Bot. Bait. ser. ii. vol. xi. pt. 1, pp. 1-209, w i tn 15 plates 

 and 77 text figs. ; 1912). — It is already known that many palms 

 exhibit a long-continued growth in thickness in which the enlargement 

 of single cells of the primary tissue takes a prominent part, but in which 

 the formation of new tissue is insignificant. Very little, however, 

 is known of the exact manner in which this growth in thickness takes 

 place, or of the extent which it attains in the different cases. More 

 over, some of the methods of study employed in the past are open 

 to criticism. The present memoir was written in order to fill, to 

 some extent, these deficiencies in our knowledge of this subject. 

 x\mongst the numerous interesting results reached by the author 

 the following may be mentioned: 



(1) In many palms there is either no secondary growth in thickness 

 of the stem or only an early-secondary growth which is already com- 

 pleted when the stem emerges from its bud-sheath. In other palms 

 a late-secondary thickening occurs ; sometimes, however, this only 

 takes place in the basal region of the stem. 



(2) So far as it has been studied, all palms show a great similarity 

 in the structure of their stem at the moment when the growth in 

 length of the stem ceases. This is due to the fact that the parenchyma 

 cells of cortex and central cylinder are isodiametric and of about 

 the same size ; the sclerenchymatous fibres are also all round in 

 section. 



(3) The thickening ring is active in only a few cases when growth 

 in length of the stem ceases ; for the secondary growth in thickness 

 this ring has little or no significance. 



(4) In one and the same stem the primary condition of the lower 

 region of the stem at an early stage is in several respects different 

 from the primary condition of the later, upper region of the stem. 

 Results obtained from the study of the upper stem-region cannot, 

 therefore, be directly applied (as some previous authors have done) 

 to explain the conditions prevailing in the lower part of the stem. 



(5) The secondary growth in thickness of palms is diffuse in 

 character in comparison with the cambial growth in thickness of 

 the Dicotyledons and Coniferae in which it is limited to a definite 

 region. 



The physiological advantages and disadvantages to the plant 

 of the diffuse method of growth in thickness are discussed by Schoute. 

 The rich branching of the stem which is found in Dicotyledons and 

 Conifers cannot take place in these stems with diffuse growth but 

 they are able to attain great height whilst they remain comparatively 

 slender. The heavy " heart-wood " of the Dicotyledons is replaced 

 in the Palms by a light, spongy tissue. — R. B. 



