ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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the protoplasm, also composer! of plasomes. In fact, all organized parts 
of the cell resemble one another in being composed of plasomes, out of 
which stationary particles, such as dermatosomes, protoplasm-granules, 
&c., are composed. 
The growth of living substance takes place either by intussus- 
ception or by apposition. Intussusception may be either cellular or 
molecular, the latter corresponding to Niigeli’s use of the term. Cellular 
apposition may take place in three modes, viz. (1) by the deposition of 
similar cell-particles, (2) by the deposition of dissimilar cell-particles, 
(3) by the apposition of cells, which is almost always combined with 
cellular intussusception. Differentiation is that process which completes 
itself in the growth of certain parts of plants, by which special portions 
of the living substance, which appear at first homogeneous, undergo a 
change, while the rest remain unchanged. 
The mode in which turgor acts in causing growth has not been 
correctly understood by previous writers. It acts not merely as a 
mechanical pressure which stretches the cell-wall, but also as an irrita- 
tion on those structures — the plasomes — on the growth and division of 
which the growth of the cell-wall, and therefore also that of the cell, 
depends by bringing about their division. 
With regard to the relationship between the cell-protoplasm and tho 
cell-nucleus, it has been shown that a differentiated nucleus is not an 
absolutely necessary constituent of the cell ; there are cases, e. g. Sac- 
cliaromyces and Nostocacese, in which the nuclear substance is distributed 
through the protoplasm. Wiesner regards tho protoplasm and tho 
nucleus as phylogenetically of the same age. The homogeneous cell- 
body of the simplest organisms forms an undifferentiated plasm, the 
archiplasrn ; from this both nucleus and protoplasm have been differen- 
tiated in the course of phylogenetic development. 
Presence of Pectic Substances in Tissues.* — M. L. Mangin gives 
an exhaustive and critical account of what has been written respecting 
the pectic substances found in vegetable tissues, and their relationship 
to the “ intercellular substance ” of Mohl, described by later writers as 
the “ primary membrane,” “median lamella,” and “ outer lamella.” His 
principal object is to demonstrate the autonomy of this group of sub- 
stances, and to justify their introduction among the fundamental 
substances of the cell-wall of the same rank as cellulose. 
The following are the chief chemical and physical reactions of this 
group of substances. They are soluble in Schultze’s reagent, and in 
caustic alkalies, but insoluble in sulphuric acid ; they are always optically 
isotropous ; they rarely give the reactions of cellulose, but sometimes 
manifest the properties of lignin. It is these substances which are 
dissolved in the processes of fermentation and putrefaction ; and it is 
they that form the “ protoplasmic ” lining of intercellular spaces. 
Wherever the production of pectic or of other allied substances takes 
place, it is connected with the process of gelification. 
* Journ. de Bot. (Morot), v. (1891) pp. 400-13, 440-8 ; vi. (1892) pp. 12-9. Cf. 
this Joumiil, 1890, p. 475. 
