ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
59 
changes which accompany germination, and the authors believe that 
bacteria take no part in its formation. 
(3) Structure of Tissues. 
Apical growth of the Stem and Leaf in Grasses.* — M. H. Douliot 
corrects his previous statement that the apical growth of the stem of 
Gramme® takes place by means of three apical cells. He now states 
that there are only two, as in many other families of Monocotyledons. 
The stem of a typical grass (e. g. Phragmites communis ) consists of three 
regions, the epiderm, the cortex, and the central cylinder. Of these one 
of the two apical cells, the terminal, gives rise to the epiderm, as well 
as to the leaves ; the other, the subterminal cell, to the cortex and the 
central cylinder. The apparent internodes of the adult stem correspond 
to the true nodes of the young stem, which have no intercalary growth. 
In the leaves of grasses the apical growth takes place by means of a 
single apical cell. 
Development of Vessels and Tracheids.'j' — Herr T. Lange contests 
the view held by Strasburger and by most writers that mature tracheae 
(vessels and tracheids) are entirely destitute of living protoplasm. 
His observations were made on a large number of Dicotyledons, Mono- 
cotyledons, Conifers, and Ferns. The distinction between the two 
classes of tracheae upheld by De Bary cannot now be maintained as 
absolute ; there are frequently transitional forms between the two. The 
method employed for detecting the presence of living protoplasm was 
that of plasmolysis ; the reagent for lignification hydrochloric phloro- 
glucin ; for protoplasm methyl-green acetic acid, borax-carmin, or eosin. 
With regard to the period at which the protoplasm disappears in 
the formation of tracheae, the author classifies the plants examined in the 
four following groups: — (1) The protoplasm disappears soon after 
the completion of the processes of thickening of the wall, lignification , 
and resorption of the septa ; (2) The tracheae contain protoplasm for a 
considerable time after their maturity ; (3) The protoplasm continues 
through the greater part or the whole of the period of growth ; (4) The 
protoplasm remains in the tracheae after the close of the period of 
growth. 
It follows from these observations that the protoplasm of the ti'ache® 
is not necessarily entirely consumed in the thickening of their walls. 
Lignification continues to take place as long as the tracheae contain 
living contents. The author maintains further that the protoplasm of 
the tracheae may take part in assimilation and metastasis. In the case 
of vessels, the protoplasts of the separate elements of which they are 
composed usually coalesce with one another after the disajipearance of 
the septa. Secondary vessels may be developed even in a zone in which 
growth has not ceased. The growth in length of an internode does not 
always cease at the same time at all points of a transverse section ; the 
hark and the epiderm often continue to grow after the wood has ceased 
to lengthen. The formation of secondary vessels in au internode which 
is still growing in length takes place in acropetal succession. 
* Ann. Sci. Nat. (Bot.), xiii. (1891) pp. 93-102 (1 pi.). Cf this Journal, 1891, 
p. 210. f Flora,- xlix. (1891) pp. 393-434 (2 pis.). 
