Geology and Natural History. 87 



The author finds structure throughout dependent upon the 

 chemical composition, thus confirming the conclusions which he 

 had previously formed from studies of the octahedral and cubic 

 irons. o. c. f. 



13. Studien uber den Milchsaft und Schleimsaft der Pflanzen ; 

 by Hans Molisch, Director of the Institute for Plant Physiology 

 at the German University in Prague. Pp. viii +111, with 33 

 text-figures. Jena, 1900 (Gustav Fischer). — Previous writers on 

 the milk-tubes of plants have studied more especially the develop- 

 ment of the tubes and the structure of their walls. In the present 

 paper, Professor Molisch gives a full account of the milky juice 

 inside the tubes, describing its microscopic structure and chemi- 

 cal composition. According to the older writers, the tubes are 

 wholly devoid of protoplasmic contents. According to the more 

 recent work of Berthold, the whole milky juice is to be looked 

 upon as a modified protoplasm. The author, however, finds neither 

 view correct, but distinguishes in the intact tubes a layer of cyto- 

 plasm, which lines the wall and which has imbedded in it numer- 

 ous nuclei, leucoplasts and vacuoles, and considers the space 

 enclosed by this layer as a sap-cavity tilled with a milky cell-sap. 

 He confirms thereby the work of E. Schmidt, who found both 

 cytoplasm and nuclei even in old tubes. In the milky juice which 

 exudes from cut surfaces, the protoplasmic elements become so 

 thoroughly mixed with the cell-sap that they cannot be distin- 

 guished. In addition to nuclei of the ordinary type, the author 

 describes a peculiar variety of nucleus to which he has given the 

 name " Blasenkern." In this the nuclear membrane is separated 

 from the nuclear substance to a greater or less extent by a space 

 filled with liquid. Since it is sometimes possible to convert ordi- 

 nary nuclei into " Blasenkerne" by the addition of water, it would 

 seem probable that the latter were abnormal, but this view is 

 not held by the author. The leucoplasts usually give rise to 

 starch-grains, but, in some cases, to solid proteids or to oil-drops, 

 both of which may also occur in the vacuoles. Other organic 

 substances sometimes found in the milky juice are caoutchouc, 

 resins, tannins, soluble proteids and carbohydrates and the recently 

 described leptomin of Raciborski. The juice of the Papaveracea3 

 contains also various alkaloids. Whether these substances occur 

 in the cytoplasmic sheath or in the sap-cavity could not always be 

 determined. The slime-tubes, which are found in certain mono- 

 cotyledonous families, show a structure very similar to that of 

 the milk-tubes, but the sap-cavity contains slime, which is only 

 occasionally milky. The nuclei are very variable in shape and 

 are sometimes drawn out into long hair-like structures. The 

 slime-tubes contain many of the substances found in milk-tubes. 

 In addition to these the author describes as new an organic body 

 to which he gives the name " luteofilin." Little could be deter- 

 mined with regard to its chemical composition. The luteofilin 

 crystallizes out of the slime in the form of sphserites, which show 

 a distinct concentric lamellation. They are soluble in water but 



