ZOOLOGY AXD BOTAXY, MICEOSCOPY, ETC. 909 



the apical growth of the cells of Bornetia scandiflora, new cap-shaped 

 pieces of cell-wall are constantly being formed at the apex, while the 

 older outer parts only continue to enlarge by stretching. 



CeU-sap and Cell-contents.* — A series of experiments on the 

 nature of the cell-sap by G. Kj-aus shows that the growth of the cell 

 is always accompanied by absorption of water, and consec^uent dilu- 

 tion of the cell-sap. The proportion of albuminoids in the cell-sap 

 decreases with the age of the internode, the proportion of free acids 

 exhibiting also a regular decrease, the sap being most acid in the 

 youngest visible internode. The absolute amount of acid, however, 

 increases with growth, acids being continually formed in the growing 

 shoot. The amount of sugar (under which term Kraus includes all 

 the copper-reducing substances of the cell-sap) increases still more, 

 both absolutely and in proportion, but attains a maximum apparently 

 before the maximum of growth. 



When a growing shoot is bent, a concentration of the sap takes 

 place at once on the convex side, the sap of the concave side becoming 

 less concentrated ; and the increased concentration is accompanied by 

 an increase in the amount of sugar, the sugar being fresh-formed at 

 the moment of disturbance, and often associated with a disappearance 

 of the free acids. Leaf-stalks exhibit the same phenomenon. 



Growth of Starch-grains,! — A. F. W. Schimper has made a fresh 

 series of experiments in the laboratory of the Johns-Hopkins Univer- 

 sity at Baltimore on the growth of starch-grains. In many parts of 

 plants which contain chlorophyll, and which are in a growing state, 

 the starch-gi'ains show certain constant peculiarities of structure. 

 They are usually disk-shaped, thick at the margins, irregularly lobed, 

 and sometimes perforated ; their thick margins are very uneven, and 

 present under the Microscope a flaky appearance, caused by the 

 sculpture of the surface, and in many cases also by vacuoles. These 

 appearances are due to a partial disintegration, in consequence of the 

 starch being partially used up for the growth of the organ, as is 

 shown by the facts that the grains formed after the retardation or 

 cessation of growth of the organ have not this character, and that a 

 similar structure is seen in the starch-grains of germinating seeds. 



After the growth of the starch-containing organ has nearly or 

 quite ceased, the formation commences of delinite forms of starch- 

 grains. Either new spherical grains are produced, having no trace of 

 the structure just described ; or those already in existence experience 

 a new growth, which however does not take place in the interior of 

 the grain, but in the form of a shining and strongly refractive layer, 

 at first thin, but gradually becoming thicker, formed around the dis- 

 integrating grain. This layer repeats at first the irregularities of 

 surface of the underlying grain ; but as fresh layers are continually 

 added, these gradually disappear, so that the siu-face is eventually 

 often quite smooth ; but even when mature, the original disintegrated 

 grain can be seen in the middle with favourable illumination. 



* Abhandl. Naturf. Ges. Halle, xv. See Bot. Ztg., sxxis. (1S81) p. 389. 

 t Bot. Ztg., xsxix. (1S8I) pp. lS5-9i, 201-11, 217-27 (1 pi.). 



