4i8 LECTVRE XXVI. 



Monocotyledons. It is advisable, in the first place, once more to regard closely ihi 

 germinating stages of the Maize-plant represented in Fig. 28 (p. 38), looking upon the 

 present figure, to a certain extent, as a continuation of that one. Here again PFis the 

 primary root, from which several thin lateral roots have originated. While, however, 

 in the dicotyledonous plant of the previous diagram the entire root-system arises from 

 the primary root, we find in this monocotyledonous plant that the primary root, 

 with its ramifications, remains small and plays an extremely subordinate part. Of 

 course as growth proqeeds the entire root-system enlarges here also, but this is accom- 

 plished by new roots ^', <i)", <^"' , springing from the lower part of the stem {s) itself, 

 the process taking place from below upwards : these roots penetrate into the earth 

 and there branch. The higher up the stem the root arises the more vigorous it- is. 

 Although these secondary roots (0' — <\/") appear at a great distance from the two 

 primary growing-points of the radicle and plumule respectively, it is nevertheless not 

 improbable that the rudiments of their growing-points were already formed long 

 before ; and that on close investigation, which of course entails great difficulties, it 

 would be possible to detect these growing-points of the roots as direct derivatives of 

 the growing-point of the shoot of the plant. However, a question is raised here 

 which will have to be taken more closely into consideration in the next lecture. The; 

 point in view now is rather to distinguish the three phases.of growth ; and here again 

 the growing-points are shaded quite black, the elongating parts grey, and those 

 which are completing their internal development and are fully grown are left 

 without shading. The leaves h — b'" of the monocotyledonous plant in question, in 

 each case envelope the whole circumference of the shoot-axis with their sheath-like 

 base ; and each younger leaf is, like the younger part of the shoot-axis, completely 

 enveloped by the sheath of every older leaf. The apex of such a shoot, therefore, 

 consists mainly. of a convolution of leaf-sheaths closely wrapped around one another, 

 and we have only to imagine these becoming thick and stout to have the whole 

 presenting the form of a bulb. It will scarcely be necessary to repeat that the 

 buds k k proceed from secondary growing-points, which in their turn originated in the 

 primary growing-point of the main shoot of the seedling. 



Immediately above the base of each leaf, the figure (Fig. 255) shows, within the 

 lightly shaded parts, certain darker transverse zones, by means of which a peculiarity 

 of the growth of this and many other plants is to be explained : ' for at these 

 zones the tissue maintains a more or less embryonic character, and its cells situated 

 further above (in the acropetal direction) gradually pass into the stage of elongation 

 and definitively complete their development. Such transverse zones at the base of the 

 internodes may be termed zones of intercalary growth ; the tissue of which they are 

 composed, however, is directly derived from the embryonic tissue of the growing- 

 point. The presence of such intercalary zones brings it about that in the plants 

 concerned the individual segments of the shoot-axis are pushed up from below out of 

 the older leaf-sheaths ; hence the youngest — i. e. the least developed — portions of the 

 internodfes are situated, not next the growing-point, but next the basal end. This 

 remarkable state of affairs, by which the processes of growth in a shoot becdme 

 still more complicated, occurs not only in many Monocotyledons, particularly 

 in all Grasses and in the flowering scapes of bulbous plants, but is extremely 

 clear also in the Horsetails (Equisetacese), among which Equisetum hyemale is 



