664 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the series of higher Cryptogams, especially in fossil forms. The so- 

 called transverse parenchyma found in Podocarpus and Cycas, which may 

 be physiologically the continuation of the centripetal wood, often plays 

 the part of support, and must be kept absolutely distinct from the centri- 

 petal wood, from a morphological point of view ; to accentuate this 

 difference, the author suggests the term transverse hydrostereome. The 

 author also gives a resume of previous work, and a critical discussion of 

 the whole subject. 



Cupressinoxylon Hookeri.* — E. A. N. Arber describes, under this 

 name, a large silicified trunk of coniferous wood from the Macquarie 

 Plains, Tasmania, preserved in the Natural History Museum. A full 

 description of the internal structure, which is in excellent preservation, 

 is given by the author. 



Cycadeoidea Reichenbachiana.j — Lester F. Ward gives a detailed 

 account of the history and geological position, and a careful description 

 of the external characters of this fossil. The specimen, which is in the 

 Museum of Mineralogy and Geology at Dresden, has been known for 

 more than two centuries and a half. It is a petrified trunk of a Cycad, 

 and the type and only known specimen of the species which it represents. 

 It has hitherto always been figured in an inverted position. The author 

 expresses regret that the internal structure of so fine and classic a speci- 

 men should never have been investigated. 



Observations on Mamillaria elongata.J — 0. V. Darbishire gives 

 an account of the anatomy of the various members of this cactaceous 

 plant, which is taken as a type of the family, and a general discussion 

 of its physiological characters, and of their relation to the conditions 

 under which the plant grows in its native habitat in Mexico. He con- 

 cludes that the spines by which the tubercles are crowned form a structure 

 which acts as a screen to protect the underlying tissues of the tubercle 

 from the strong sunlight. Such an organ may be called a paraheliode. 

 A similar function is played by the set of hairs found at the top of the 

 leaf of Mesembryanthemvm stellatum. He finds that the development of 

 palisade-tissue is regulated by the influence of the light on the processes 

 of photosynthesis; while the depth, but not the extension of the air- 

 spaces, is dependent on the conditions favourable or otherwise to tran- 

 spiration. The tubercle of Mamillaria represents morphologically the 

 leaf -basis, with perhaps a portion of the stem. The sp nes are modified 

 portions of the leaf -blade. There is only one bud in connexion with each 

 tubercle, and that is axillary to it. The author insists that the guiding 

 principle which underlies the adaptation of plants, and the production of 

 plant forms, is physiological. There is no evidence to show that direct 

 protection against attacks by animals influences the development of any 

 plant-form. 



Germination and Formation of the Primary Root in Palms.§ — C. L. 

 Gatin has studied germination iiuspecies of Phoenix and Archontophamix 



* Geol. Mag., dec. V.. i. (1904) pp. 7-11 (1 pi. and 2 figs, in text). 



t Amer. Journ. Sci., xviii. (1904) pp. 40-52 (1 fig.). 



X Ann. Bot., xviii. (1904) pp. 375-416 (2 pis.). 



§ Rev. Gen. Bot., xvi. (1904) pp. 177-87 (7 figs, in text). 



