THE PHASE OF EMBRYONIC GROWTH. 4I9 



particularly distinguished in that the internodes are each year slightly pushed up 

 from below out of the older leaf-sheaths. Similar peculiarities occur moreover in 

 some Dicotyledons — e. g. the Polygoneae, Umbelliferae, &c. 



In the Grasses and Liliaceae (and in a less degree also elsewhere) there occurs 

 combined with this intercalary growth of the internodes a very similar process in 

 the leaves. These also go on growing at their basal parts, which are in the phase of 

 elongation when the apex of the leaf has long been completely developed : they 

 become, so to speak, pushed up from below out of the body of the plant, as may 

 very easily be observed in Hyacinths in the spring. 



It will not be diflScult for the reader to discover the points common to the two 

 diagrams described. These points in common, moreover, we may regard as the type 

 of growth prevailing in the vegetable kingdom. It exists almost without exception in 

 the Mosses and Vascular plants; and we find it in its simplest features in many 

 Algae and even in some Fungi. Nevertheless, as follows from what has been said 

 on p. 84, and may be illustrated by fiirther examples {e.g. MacrocysHs, &c.), 

 entirely different distributions of the phases of growth may occur among the Algse 

 and Fungi ; these, however, remain confined to a few small groups and will therefore 

 be passed over here. 



After this preliminary sketch, I now proceed to a more exact description of the 

 three phases of growth. 



(i) The condition of embryonic growth in the growing-points is distinguished 

 chiefly by the following characters : — 



The development of new organs takes place exclusively in the growing-points. 



The growth of the young organs at the growing-point, both with respect to the 

 increase in volume and the changes in form, is exceedingly slow. 



The mass of a growing-point, from which the very large volume of tissue of an 

 entire shoot or root-systefii proceeds finally, is for and by itself extremely small, and 

 but very rarely amounts to i^th of a milligram. 



This small quantity of matter is continually being regenerated by the addition of 

 suitable nutritive substances ; while the basal portions of the growing-point gradually 

 pass over into the condition of elongation, and then into permanent tissue. 



The growing-points, as well as their outgrowths — i. e. the young organs in 

 an embryonic condition — consist of a cell-tissue which is usually termed primary 

 meristem, but is better distinguished as embryonic tissue. 



The embryonic tissue of the growing-point and very young organs forms a solid, 

 somewhat hard, and occasionally even brittle mass, which consists essentially only of 

 protoplasm and the substance of the cell nuclei ; the cell-walls being extremely thin. 

 These substances are, it is true, permeated with water ; but fluid cell-sap in the form 

 of so-called vacuoles is not present, or only in very small quantity. 



The cells of the embryonic tissue are very small, tHe nuclei, on the contrary, 

 being relatively vety large, and their rounded form adapted to the shape of 

 the cells. If the latter are tabular, the nucleus is flattened like a cake ; if cubical, 

 the nHcleus is spherical; if cylindrical or prismatic, the nucleus is elongated also. 

 The nucleus, however, always forms a very considerable portion of the mass of the 

 cell ; and thus the embryonic tissue is chiefly characterised by the predominance of 

 the substance of the nuclei, in which, again, nuclein plays a chief part. 



