96 Mr. H assail on MohVs views 



an almost insensible transition is formed, from manifest angu- 

 lar cells even to the grains themselves/' Here I would ob- 

 serve that Mohl has already recorded his belief that the large 

 granules in one plant are really cells, for example, in Fit- 

 cairnia latifolia. " We now come to facts calculated to pro- 

 duce the admission, that the external membrane is not only 

 made up of grains resembling each other, but that there is 

 formed in it moreover a substance half membranous, half ge- 

 latinous. There are cases, where these grains, w^hen the pol- 

 len is extended by the imbibition of w ater, do not touch each 

 other ; but instead of being pressed one against the other, as 

 in most pollen, they appear scattered upon a membrane smooth 

 and uniform, for example, in Plumbago C(Brulea,Jatropha urens, 

 &c. It happens also sometimes, that in causing the grain of 

 pollen to roll in a drop of water, between two small plates of 

 glass, that some portion of the external membrane is detached 

 from the granule which it surrounds, and that this part pre- 

 sents the appearance of a uniform (homogeneous) and colour- 

 less membrane. Moreover, as we shall show further on, the 

 external membrane of most pollen presents regular plaits, 

 which are effaced by the extension of the grain in w^ater. 

 Upon the part which in the dry pollen is concealed by the 

 folds, the grains are altogether wanting, or form groups scat- 

 tered at great intervals, so that the grains are placed upon a 

 uniform membrane, and are separated one from the other by 

 the extension of that membrane. It is not an uncommon cir- 

 cumstance to find the external membrane, at the situations 

 where it covers the papilliform processes of the internal mem- 

 brane, deprived of grains and completely uniform. Whether 

 even these proofs shall bedeemed sufficient, as Inowthink them 

 to be, to establish the analogy of structure and of functions be- 

 tween the well-formed cells and these grains, it is neverthe- 

 less, at all times, but an analogy, and we have no right to re- 

 gard them as cellular tissue itself, but only as the rudiments 

 of cells. The granular disposition of the external membrane 

 is by much the most frequent. As we have met wdth gradual 

 transitions from the membrane plainly cellular to the granu- 

 lar and dotted membrane, in the same manner, this itself does 

 not always present itself equally well-formed, and we find in 

 many species grains becoming smaller and smaller, until the 

 membrane becomes almost completely smooth and homoge- 

 neous, and thus presents a striking resemblance with the mem- 

 brane of ordinary vegetable cells. This is the case, for ex- 

 ample, in Allium fistulosum, Chamcerops humilis, Araucaria im- 

 bricata, Rumeoc scutatus, Morina persica, in the Boraginaceas, 

 Chenopodece, Myrtacece, Graminacea^i in Rivina brasiliensis, &c. 



