4IO NATURAL SCIENCE. june, 



ing 1 8 feet in height, but this is confined to the high altitudes. It 

 is in the shrubby vegetation that the arid character is most reflected. 

 The largest of the shrubs, the creosote-bush {Larrea tridentata) com- 

 monly grows to from three to five feet, while the height of most desert 

 species ranges from this down to a foot. The struggle for continued 

 existence is not with each other, as in a humid climate, since from 

 scarcity of moisture each individual is separated by several yards 

 from its neighbours, but against physical forces alone. A rounded 

 form is the result of this spacing out, as, surrounded on all sides by 

 light, the plants develop equally in every direction. No creeping or 

 cone-shaped shrub is known in the desert. 



An important principle in plant-life is the absorption of moisture 

 from the soil by the roots, its conduction along the stem, and its 

 transpiration from the leaf-surface ; hence the study of desert plants 

 reveals various adaptations for striking a living balance between 

 absorption and loss of moisture. One device is great root develop- 

 ment ; thus the roots of the mesquite [Prosopis jxiUflora), a tree 

 characteristic of desert areas with a moist subsoil, grow to enormous 

 lengths ; one was seen which reached more than i6 yards. As, 

 however, during the season of drought the largest amount of water 

 that can be absorbed is comparatively small, the greatest modifica- 

 tions are found m the stem and foliage. The size, form, and thick- 

 ness of the leaves are most concerned. Thus, of forty-one shrubs 

 examined, only four had leaves whose single-surface area exceeded a 

 square centimetre. In some cases the leaves fall soon after the 

 cessation of the spring rains, but in most they remain for the greater 

 part of the summer, and to reduce loss of water to a minimum, have 

 their surfaces protected by a resinous excretion or a covering of dry 

 hairs. The creosote bush, for instance, owes its name to the 

 resinous covering, in appearance like shellac, of its leaves and small 

 twigs. 



The twenty-one excellent plates of new species will serve to 

 illustrate some of these points, and the large map at the end of the 

 volume on which the route is indicated is also a valuable addition. 



The Hatching of the Octopus. 



That an Octopus should be given to sit upon its eggs for the 

 purpose of hatching them, like any barn-door hen, savours at first of 

 the ludicrous, even though the instance of the female Argonaut which 

 carries, if it does not incubate its eggs in its "boat," be borne in 

 mind. More curious still is it that the habit was first observed and 

 recorded by that astute old-time philosopher Aristotle, but subse- 

 quently forgotten till the discovery the other day in Lower California, 

 by M. Diguet, of a new species of Octopus, which sets to work in a 

 very systematic fashion, brought the circumstance once more to light. 

 Aristotle remarked that the Octopus sits as soon as all its eggs are 



