412 Dar bishire, — Observations on Mamillaria elongata . 
plants really the results of efforts on the part of the plant for self- 
protection ? * 
Coville, F. V., and MacDougal, D. T. : Desert Botanical Laboratory 
of the Carnegie Institution, Washington, 1903. This first report of the 
Desert Laboratory is naturally of a preliminary character ; but it contains 
some excellent photographs, a brief account of some valuable observations, 
and also a useful Bibliography. 
The main results obtained during the preparation of this paper may 
be briefly summed up thus. 
(1) The set of spines by which the tubercles of Mamillaria elongata 
are crowned, form a structure which acts as a screen, protecting the 
underlying tissues of the tubercle from the strong sunlight. Such an organ 
may be called a paraheliode. 
The set of hairs found at the top of the leaf of Mesembryan themum 
stellatum also form a paraheliode. The large cells of the epidermis of the 
same plant are also paraheliode structures. 
(2) The development of palisade-tissue is governed by the influence 
of the light on the photosynthetical processes, the depth, but not the 
extension of the air-spaces, is dependent on the conditions favourable or 
otherwise to transpiration. 
(3) The tubercle of Mamillaria elongata represents morphologically 
the leaf-basis, and possibly in addition a portion of the stem. The spines 
are modified portions of the leaf-blade. There is only one bud in 
connexion with each tubercle or leaf, and that is axillary to the leaf, i. e. 
the tubercle. 
(4) 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. 
The foregoing remarks on Mamillaria elongata may, as regards the 
physiological results, be made to include, though in a form varying with 
specific peculiarities, most of the other members of the natural order 
Cactaceae, the structure of which is remarkably uniform. 
University of Manchester. 
Literature. 
1 . Areschoug, F. W. C. : Ober die physiologischen Leistungen imd die Entwickelung des 
Grundgewebes des Blattes. Kongl. fysiografiska sallskapets i Lund Handlingar, Ny 
foljd, Band 8, 1897. 
2 . Askenasy, E. : Uber die Temperatur, welche Pflanzen im Sonnenlicht annehmen. Botan. 
Zt g-> 1875, p.441. 
3 . Aubert, M. : Recherches physiologiques sur les plantes grasses. Paris: Masson, 1892. 
