LECTURE XXVII. 



RELATIONS BETWEEN GROWTH AND CELL-DIVISION IN THE 

 •EMBRYONIC TISSUES. 



Growth — i.e. the increase in volume and change of form — may take 

 place in plants even without accompanying cell-divisions. In this connection, 

 I have already repeatedly referred to the non-cellular plants, such as Boirydium, 

 Caulerpa, Vaucherta, etc., and particularly to the Myxomycetes. It is important 

 to bear this fact in mind ; because it proves that the formation of cells is a pheno- 

 menon subordinate to, and independent of, growth. The excessive importance for 

 organic life hitherto ascribed to cell-formation found expression in this direction also, 

 in that it was believed that growth depended upon the formation of cells. This is, 

 however, not the case. On the other hand, however, the fact i_s of course important, 

 that while a few hundred simple forms of plants exist in which growth is not accom- 

 panied by cell-division, in all other plants growth and cell-division are intimately 

 connected with one another. In attempting, then, to make cleat the relations of 

 the two processes — growth and cell-division — it is above all to be insisted upon 

 that growth is the primary, and cell-division the secondary and independent 

 phenomenon. 



The following is an epitome of a detailed investigation of the matter which I 

 published in 1878-79^- The matter here depends upon geometrical, and in part 



' We owe the first investigations which laid the foundations as to the relations between growth 

 and cell-division, as so much of the best of our literature, to Naegeli's ingenious researches ; he 

 started with a series of treatises on this subject in his ' Zeitschrift fiir wissenschaftliche Botanik,' 

 published with Schleiden, in 1844-1846, a literature consolidated by numerous observers in still more 

 numerous treatises. All Naegeli's successors, however, held exactly to the scheme established by him, 

 according to which also Schwendener, with Naegeli's co-operation, further represented the relations 

 between growth and cell-division in their book ' Das Mikroskop^ II. Aufl. 1877, pp. 544, &c. 



I established the point of view explained in my lecture, and which has given an entirely different 

 turn to the ideas concerning this subject, in my treatises, ' Uber die Anordnung der Zellen in jiiugsten 

 Pflanzentheikn' (Arb. des bot. Inst, in Wzbg. B. II, H. I, 1878) and ' Cber Zellenanordnung und 

 Wachsthum' (ibid. H. i, 1879). 



In the first-named treatise I sought to give precision to my view as to the processes of growth in 

 growing-points and other embryonic masses of tissue by stating (p. 52), ' If we abstract from the 

 so-called individuality of the cell, and pay attention only to the course of the layers which cross one 

 another in three directions, we obtain a structure which may be compared with the internal structure 

 of a much thickened cell-wall. The three systems of layers in the growing-point correspond to the 

 aystem of concentric layers and the two systems of so-called striation of the cell-wall, as they have 

 been described by Naegeli. Stratification and striation of the cell-wall, as is known, depend oil a. 

 regular alternation of denser and less dense substance in three directions, -Which cut one another, aS 



