CIRCULATION OF SAP IN PLANTS. 351 



Is easily separated entire from the joint. It then appears 

 to be exactly round, nearly lenticular, and its granular 

 matter is either held together by a coagulated pulp not 

 visibly granular, or, which may be considered equally pro- 

 bable, by an enveloping membrane. The analogy of this 

 nucleus to that existing in the various stages of develop- 

 ment of the colls in which the grains of pollen are formed 

 in the same species, is sufficiently obvious. 



In the joint of the same, when immersed in water, 

 being at the same time freed from air, and consequently 

 made more transparent, a circulation of very minute 

 granular matter is visible. This requires at least a J power 

 to show it well. The motion of the granular fluid is 

 seldom in one uniform circle, but in several apparently 

 independent currents : and these again, though often 

 exactly longitudinal, and consequently in the direction of 

 the striae of the membrane, are not unfrequently observed 

 forming various angles with these striae. The smallest of 

 the currents appear to consist of a single series of granules. 

 The course of these currents seems often in some degree 

 affected by the nucleus, towards or from which many of 

 them occasionally tend or appear to proceed. They can 

 hardly, however, be said to be impeded by the nucleus, 

 for they are occasionally observed passing between its 

 surface and that of the cell ; a proof that this body does 

 not adhere to both sides of the cavity, and also that the 

 number and various directions of the currents cannot be 

 owing to partial obstructions arising from the unequal 

 compression of the cell. 



Flower-buds. "In the very early stage of the flower- 

 bud, while the anthera are yet colourless, their loculi 

 are filled with minute lenticular grains, having a trans- 

 parent flat limb, with a slightly convex and minutely 

 granular semi-opaque disc. This disc is the nucleus of 

 the cell, which probably loses its membrane or limb, and, 

 gradually enlarging, forms in the next stage a grain also 

 lenticular, and which is marked either with only one 

 transparent line dividing it into two equal parts, or with 

 two lines crossing at right angles, and dividing it into four 

 equal parts. In each of the quadratures a small nucleus 

 is visible ; and, even where one transparent line is only dis- 



