234 CONTRIBUTIONS TO 



tyledons, in the leaf, stem, and their metamorphosed parts. 

 The largest which I have seen measured 00022 Paris inch in 

 diameter (in Fritillaria pyrenaica) ; the smallest, in the em- 

 bryonal extremity of the pollen-tube of Linum pallescens, from 

 0*00009 to 0-0001 Paris inch. In the albumen of Abies excelsa 

 I found the average of several admeasurements of examples, 

 which appeared of equal size, to be 0-00034-0-00059-000079. 

 In the young leaves of Crassida portulaca, 0-0003 ; and in the 

 albumen of Pimelea drupacea, 0-00095-0-001055. Little im- 

 portance, however, can, on the whole, be attached to these 

 admeasurements, since they increase and diminish, and we 

 cannot determine in what period of its existence the cytoblast 

 may be at the time. 



Its internal structure is in general granulous, without, how- 

 ever, the granules, of which it consists, being very clearly dis- 

 tinct from each other. Its consistence is very variable, from 

 such a degree of softness as that it almost dissolves in water, 

 to a firmness which bears a considerable pressure of the com- 

 pressorium without alteration of form. The more recent its 

 formation, the softer it is; and this also applies to cases in 

 which its existence is merely transitory. It is denser and more 

 sharply defined when it endures throughout the whole vital 

 process of the plant as a permanent tissue, as in the Orchidete. 



These peculiarities have been more or less fully described 

 by R. Brown (Organs and Mode of Fecundation in Orchidese 

 and Asclepiadese ; Linn. Trans. 1833, p. 710), and recently by 

 Meyen (Physiologie, &c, Bd. I, p. 207). A phenomenon, how- 

 ever, has escaped both of these most acute observers, which I 

 am notwithstanding disposed to regard as one of the most 

 essential. In very large and beautifully developed cytoblasts, 

 for example, in the recently formed albumen of Phormium 

 tenax and Cham&dorea schiedeana (pi. I, fig. 5), there is ob- 

 served (whether sunk in the interior or on its surface, is not 

 yet clear to me) a small, sharply defined body, which, judging 

 from the shadow that it casts, appears to represent a thick 

 ring, or a thick-walled hollow globule. In examples which are 

 not so well developed, only the external sharply defined circle of 

 this ring can be observed, and in its centre a dark point ; for 

 example, in the stipes of the embryo of Limnanthes Douglasii, 

 Orchis latifolia (pi. I, fig. 21), Pimelea drupacea (figs. 14, 15). 



