28 THIRD REPORT — 18S3. 



have already reduced our knowledge of the exact internal struc- 

 ture of plants to a state of very considerable precision; although 

 it must be confessed that vegetable anatomy is still the field 

 where the greatest discoveries may be expected. 



It is now genei'ally agreed that the old opinions, that the tis- 

 sue of plants is either a membrane doubled together in endless 

 folds, or a congeries of cavities formed in solidifiable mucus 

 by the extrication of gaseous matter, are equally erroneous, 

 and that it really consists of distinct sacs or cells, pressed to- 

 gether and adhering to each other by the sides where they are 

 in contact. 



It is considered that this is proved by the following circum- 

 stances. 1. By the action of some powerful solvent, such as 

 nitric acid, the cells may be artificially separated from each 

 other. 2. In parts which become succulent, the cells separate 

 spontaneously, as in the receptacle of the strawberry, the berry 

 of the privet, &c. 3. When the parts are young, their tissue 

 may be easily separated by pressure in water. 4. It is con- 

 formable to what has been observed in the growth of plants. 

 Amici found that the new tubes of Chara appear like young buds 

 from the points or axillae of pre-existing tubes ; an observation 

 that has been confirmed by Mr. Henry Slack*. It has been 

 distinctly proved by M. Mirbelf, that the same thing occurs in 

 the case of Mar chantia poly morpha. That learned botanist, in 

 the course of his inquiries into the structure of this remarkable 

 plant, may be said to have been present at the birth of its cel- 

 lular tissue ; and he found that in all cases one tube or utricle 

 generated another, so that sometimes the young masses of tis- 

 sue had the appearance of knotted or branched cords. He satis- 

 fied himself, by a beautifully connected series of observations, 

 that new parts are not formed by the adhesion of vesicles origi- 

 nally distinct, as many have asserted, but by the generative 

 power of one first utricle, which engenders others endowed with 

 the same property. 



It appears that when first formed the sacs are completely 

 closed np, so that there is no communication between the one 

 and the other, excepting through the highly permeable mem- 

 brane of which they are composed. This, indeed, is not con- 

 formable to the observations of those who have described and 

 represented pores or passages of considerable magnitude pierced 

 in the sides of the sacs; but it has been satisfactorily shown by 

 Dutrochet, that the spaces supposed by such observers to be 



* Transactions of the Society of Arts, vol. xlix. 



f " Rechorches Anatomiques et Physiologiques sur le Marchantia ■polyinor- 

 ■pha," in Nouv. Ann. du Museum, vol. i. p. 93. 



