256 



ON THE DIRECTION OF PLANTS. 



" At Dimchurch," says Mr. Smith, " the dyke was filled with the plant, and 

 I was surprised to observe pollen scattered over the surface of the water, and small 

 yellow spikes of flowers rising above its level ; many of these had discharged their 

 pollen ; in a few the elevated anthers were still entire. Sir J. E. Smith and Dr. 

 Hooker, therefore, are wrong in asserting that the impregnation takes place beneath 

 the water, and within the sheath of the leaves, before the elongation of the flower 

 stalks. On the contrary, these are universally elongated before the anthers burst, 

 the contacts of atmospheric air being necessary to fecundation. The anthers are 

 vesicular and buoyant : as they swell and become mature, the membranous sheath 

 inclosing them is distended, and the whole is brought to the surface of the water. 

 The flower stalks are rapidly lengthened ; the flowers quit the sheath, which then 

 becomes a bladder, and aids the elevation of the spike an inch above the water. 

 Presently the anthers burst, the vesicle loses its buoyancy, and the flower stalk 

 bearing the fertilised stigmas sinks within the bosom of the parent plant. The 

 stigmas are rarely four only, usually four to six. 



We need say no more to recommend this interesting work : the 

 preceding extract alone will be sufficient for that purpose to every 

 philosophical reader. 



ON THE DIRECTION OF PLANTS. 



BY PROFESSOR DE CANDOLLE, OF GENEVA. 



The roots of plants are lengthened out only by their extremity ; the 

 growing point of each root is then in a state of softness, which may be 

 compared to semifluidity. The constant action of gravitation should 

 therefore force it to descend ; the energy with which each root will 

 tend to direct itself towards the centre of the earth will be in proportion 

 to the degree of softness of its growing extremities. The stems increase 

 in a given time by the whole length of their shoot. But let us see 

 what happens in a branch with an obliquity of any kind ; when this is 

 the case, it is manifest that a portion of the lymphatic and nutrient 

 juices, as they pass through the intercellular passages, are drawn by 

 gravity towards the inferior side of the branch, and that as a con- 

 sequence this side receives a greater quantity of nutriment than the 

 superior part. The proof of this assertion is, that the superior part of 

 an oblique branch is always thicker than the inferior part, or, in other 

 words, the medullary canal of an oblique branch is a little nearer the 

 superior side, because its inferior layers are more grown. This dis- 

 proportion between the increase of the superior and inferior layers will 

 be the more strongly marked according as the branch is nearer a hori- 



