980 SUMMARY OF CURUENT RESEARCHES RELATING TO 



statement that the mass of the spindle-fibres cliifors chemically from the 

 cytoplftsm — not containing any substance incapable of digestion— and 

 therefore cannot result entirely from the entrance of the cytoplasm into 

 the nucleiis. Pollon-mother-cells of Hemerocallis freshly observed in 

 white of egg show clearly that the nuclear cavity is, by its homogeneous 

 character, sharply distinguished from the non-liomogonoons cytoplasm. 

 Zacharias dissents also in some points from Sti'asburger's conclusions 

 respecting the constitution of the unitiug-threads and the function of the 

 nucleoli. 



Strasburger explains the act of impregnation as depending on a union 

 of similar nuclear threads, the further development of which is excited 

 by the mixing of the nuclear sap. Zacharias considers the part assigned 

 to the nuclear sap to be unsupported by direct observation ; ami that the 

 former portion of this statement is rather a description of the last stage 

 in the process of fertilization. 



Properties and Chang-es of the Membrane, Protoplasm, and Nucleus 

 of Plant-cells.* — Prof. C. Frommann has a series of essays in which ho 

 deals with p( iuts ccinnected with plant-cells. The first is devoted to 

 some structural relations observed in the membranes of the epidermis of 

 the leaves of Bracxna draco and Euphorbia cyparis^'ias. He comes to 

 the conclusion that the filamentar structures or networks whicli belong 

 to the membrane and are sometimes connected with the intracellular 

 protoplasm, sometimes resemble those of the latter, and are sometimes 

 much firmer and more refractive ; the intermediate substance is some- 

 times feebly, and sometimes highly refractive ; in the latter case it may 

 be the cause of the protoplasmic parts becoming indistinct or disap- 

 jiearing ; in homogeneous membranes the protoplasmic structures which 

 belong to the foundations of the membrane may be made visible again 

 by the use of reagents which cause considerable swelling. It must not, 

 however, be supposed that all homogeneous membranes inclose networks 

 or fibrillar structures which belong to the protoplasm. The appearance 

 of large rounded sj^indle-shaped or irregularly formed and partly ana- 

 stomosing structures, such as the author has detected in the side-walla of 

 Dracsena, lead to the belief that, within circumscribed areas, networks 

 of protojilasm first fuse with one another to form homogeneous bodies ; it 

 is only after tliis that cellulose is foi'mcd in them. That membranes 

 are really formed in this way from homogeneous protoplasmic layers is 

 shown in the ossa}'' which treats of the formation of cellulose-membranes 

 within the intercellular spaces and the cells of the parenchyma of the 

 knobs of Cyclamen and Phajns. 



The appearance of chlorojihyll in cell-membranes has been studied ; 

 sections and surface-views show that the cuticle in a number of places 

 either becomes thickened, and beset with knot-like or wart-likc growths, 

 or it becomes considerably swollen and softened. In the latter case fine 

 granules and filaments become differentiated and often connected together 

 by plexuses of delicate meshwork. Vacuoles appear at the same time. 

 The layers thus formed extend into the adjoining unaltered or only 

 slightly thickened cuticle. In addition, we find prominent aggregations 

 of granular filamentar substance ; from these, newly-formed parts may 

 be differentiated which fuse with those already present. But, when this 

 occurs, several of the green layers are found to have their boundaries 



* JeuaiscJi. Zcitschr. f. Naturwiss., xxii. (1888) pp. 17-174 (5 pis.) 



