NOTES 71 



celled to the many-celled condition; but they do exemplify certain intermediate 



states, and thus give some insight into the stages by which the transformation has 



in all probability taken place in the course of evolution. 



Let us first consider the case of juxtaposed initials. There can be uo doubt thai 

 the paired apical initials of Selaginella Wallichii, first described by Strasburger, 

 have originated from a single four-sided (pyramidal) initial, owing to the appearance 

 of a median longitudinal partition. It seems natural to assume that the four juxta- 

 posed initials discovered by Schwendener in the roots of Marattiaceae have likewise 

 arisen from a single apical cell, which has become divided into quadrants by two 

 radial walls placed at right angles to one another. (This view was put forward 

 tentatively in the first [German] edition of this book ; it has since been proved 

 to be correct by Koch in the case of Angiopteris evecta.) 



The primordial meristem with superimposed initials can also be easily derived 

 from that in which there is a single apical cell. This point has already been discussed 

 by the author (I.e. [38] ) in the following words : " If, for example, we imagine the 

 three-sided (pyramidal) apical cell of a Fern-stem to become subdivided by two 

 transverse walls into three superimposed compartments, and if we further suppose 

 each of these compartments to go on growing and cutting off segments after the 

 manner of the single original initial, we arrive at the type of growing-point charac- 

 teristic of the lateral shoots of Ceratophyllum. If the original initial were subdivided 

 into two superimposed portions, we should obtain the structure which jjrevails in 

 the young dichotomous leaf-segments of this plant. In Ceratophyllum the appro- 

 priate partition walls are there from the first. It is quite possible, however, that 

 in other instances they are not laid down until the young leaves or shoots are becoming 

 marked off from the main apex ; it is cases of this kind that should be particularly 

 sought for." 



After what has been said, there should be no difficulty in imagining how the 

 growing-point with both juxtaposed and superimposed initials can be derived from 

 that with a single apical cell. 



In conclusion, we may enquire into the causes underlying the evolution of the 

 complex from the simple type of growing-point ; in regard to this question it is 

 at present impossible to do more than put forward certain suggestions in very general 

 terms. It will readily be admitted, for instance, that the individuality of the initial 

 is much more pronounced where there is a single apical cell, than where there are 

 several. This follows at once from the great regularity of the segmentation, and the 

 constancy of the cell-shapes, in growing-points which possess a single initial. The 

 transition from the simple to the complex type of structure thus involves a limita- ' 

 tion of the independence of the individual cell in the interests of the whole organ. 

 On the whole, this subordination of the cell becomes more pronounced as one ascends 

 the scale of evolution ; it is, therefore, not surprising to find the single apical cell of 

 the Pteridophytes replaced by a group of initials among Phanerogam* and especially 

 in the Angiosperms. 



VI. Hanstein : Festschr. niederrhein. Ges. 1868. Id. Hanst. Bot, Abb. 1, 1870. 



42. Apical growth of roots. Nageli und Zeitgeb, Beitr. 1, 1867. Hanstein: Hanst. 

 Bot. Abh. 1, 1870. Reinke : Hanst. Bot. Abb. 1, :>. Janczewski : Ann. Sci. Nat., 

 ser. V., 20. Holle : B.Z. 1876. Treub : Le meristeme primit. d. 1. racine dans 1. 

 Monocotyledones, Leiden, 1S76. Eriksson : P.J. 11, 1878. Flahault : Ann. Sci. 

 Nat., ser. VI.. 6. Schwendener : Sitzb. Berlin, 1882. Van Tieghem : Journ. de 

 Bot. 1, 1887. Van Tieghem et Douliot, Ann. Sci. Nat., ser. VII., 8, 1888. Strasburger : 

 Botanische Praktikum \Ai\\ ed.), pp. 323 sqq. A number of interesting observations 

 on the root-cap of aerial roots will be found in a paper by Alalar Richter : Bibl. 

 Bot. No. 54, 1U01. 



