422 SUMMARY OF CORRENT RESEARCHES RELATING TO 



ficd an attempt made to explain it on the main assumption of the book. 

 The arrangement referred to is a consequence of exchanges (diffusion, 

 absorption, &c.) with the environment : passive particles snsijended in the 

 cell would have to assume positions which are definite ; active particles 

 (i. e. particles which themselves exchange with the layer in v/hich they are 

 imbedded) might interfere with the simple shell arrangement, and we 

 have systems within a system. After examining what occurs in the case of 

 a spherical system or cell, the author extends the analysis to an ellipsoid 

 and other anisodiametric systems, and finds the resulfs accord with what is 

 found in nature. The question of the " Hautschicht " is then attacked, 

 and De Vries' late statements as to the existence of a pellicle or " wall " 

 around the vacuole are criticized. Berthold condemns this pellicle as an 

 artificial product — a "precipitation-membrane" — in many if not inmost 

 cases. 



The fifth chapter is concerned with showing that, in spite of the great 

 variety of forms exhibited by the chlorophyll-bodies of different plants, 

 especially Algfe, their position, consistence, changes in form, division, &c., 

 can be explained in accordance with the view that they are parts of an 

 emulsion. Other cell-contents are considered also, oil-drops, tannin, 

 nucleus, vacuoles, &c. The chlorophyll-corjiuscles of higher plants are 

 compared to drops resting on a substratum which they do not wet, their 

 shape being in part due to radial pressures. 



The division of chlorophyll-corpuscles is then examined, and this leads 

 to the division of the nucleus and cell, which is treated separately. A 

 spherical mass of fluid must increase its surface if it divides ; this implies 

 a diminution of tension at the common surface (as wdth the formation of 

 pseudopodia), and concentric shells in the medium or in the mass of fluid 

 in question. All the conditions fulfilled, pseudopodia can be formed either 

 from the medium into the mass, or from the mass into the medium. An 

 annular pseudopodium would divide the spherical (or spheroidal) mass 

 into two. 



This leads to the sixth chapter, where, after reviewing the process of 

 cell-division generally, the author separates the essential from the unes- 

 sential processes, and agrees with Strasburger that the division of the 

 nucleus must be regarded as an accompanying phenomenon. The division 

 of the ovum of Echinus and Ciona is described : soon after the male and 

 female nuclei have ftised, two centres appear in the egg, each with radii — 

 the required bi-polarity is established. The exchanges and movements in 

 the protoplasm are then followed ; the result is that certain constituents 

 accumulate to excess in the equator between the two radiating centres, or 

 " suns." The two " suns " are the centres of the future daughter-cells ; the 

 still single nucleus lies between them in a bridge of the same protoplasm 

 as that in which the " suns " are imbedded : the more peripheral protoplasm 

 of the cell (ovum) has accumulated chiefly round the nucleus— i. e. in the 

 equatorial plane. This equatorial protoplasm then begins to cut in two the 

 nucleus, which has assumed the " karyokinetic " condition. The superficial 

 shells of protoplasm are assumed to put forth pseudopodia between the 

 " suns " — i. e. the author regards it as fundamentally a wetting process, 

 due to changes at the surfaces; the processes are essentially of the same 

 nature in vegetable cells. 



The seventh cha2)ter treats of the cell-network of plants, and the direc- 

 tions of cell-divisions, &c. It is in great measure a criticism of Sachs's view 

 of the structure of the higher plants. Two main principles are employed. 

 (1) The cell-divisions are, as a rule (at least in growing-points, &c.), 

 halvings — i. c. each daughter-cell has the same cubic contents. The shaje 



