420 LECTURE XVII. 



attaches itself by this end, which accordingly becomes the 

 base of the new plant. The egg or oospore from which the 

 body of Fucus is developed does not present this distinction 

 of two ends, this polarity as we may term it, and, inasmuch as 

 it is spherical, it is not easy to ascertain whether or not it is 

 always one particular area of the surface of the egg which 

 becomes attached and constitutes the base of the young plant. 

 However this may be, it is certain that that portion of its 

 surface which becomes attached always becomes the base, and 

 the diametrically opposite surface always becomes the apex, 

 of the young plant. In the case of the Vascular Plant, we 

 find, as I have elsewhere pointed out, that, in the development 

 of the embryo, primary stem and primary root, when these 

 members are present, are always developed from diametrically 

 opposite segments of the egg or oospore. Taking all these 

 facts into consideration, it may be fairly concluded that the 

 distinction of base and apex and, in Vascular Plants, the 

 opposite direction of growth of primary stem and primary root 

 are not induced by any external influences but are inherent in 

 the plant. In the case of Oedogonium, where the repro- 

 ductive cell itself already presents evident polarity, the 

 polarity is impressed upon it by the parent plant. 



In contrasting just now the general morphology of a 

 Fucus with that of a Vascular Plant, we compared the body 

 of the former to a cone standing on its base, and that of the 

 latter to two cones joined by their bases, the apex of the cone 

 being in all these cases ^punctum vegetationis. We will now 

 somewhat increase the complexity of our conception of the 

 plant-body. We will imagine that the single case which 

 corresponds to the main body of Fucus, and the two cones 

 constituting that of the Vascular Plant, bear other cones upon 

 their flanks, these lateral cones being attached by their bases 

 and having their apices free. These cones may be taken 

 to represent lateral branches, which, like the parent-member, 

 present a distinction of base and apex, and each of which 

 possesses a growing-point at its apex. We obtain in this 

 way a simple idea of the composition of a plant-body in which 

 branching takes place, 



