4 THE PRESIDENTIAL ADDRESS. 



highly complex shoots and roots, so necessary for acquiring food directly 

 from the air and soil. We may further contrast the genesis of the indi- 

 vidual in either case. In the mammal the parts are formed once for all, 

 its embryology being an incident closed early in the individual life ; but 

 in the tree embryology may be continued for centuries, and is theoretically 

 unlimited, except by death ; during life it has the power of producing 

 leaves and branches from every distal bud. The fact is that, though 

 certain underlying principles are the same for both kingdoms, the working 

 out has been distinct from the first. Hence, the morphology of plants 

 must stand on its own feet ; indeed, it has been said with some degree of 

 truth that whenever botanists have borrowed their morphological outlook 

 from the sister science they have gone wrong. 



The normal development of a multicellular plant starts from the 

 fertilised egg, and elaboration, both external and internal, follows on 

 increasing size. Polarity, that is the distinction of apex and base, is defined 

 in most plants of high organisation by the first cell-cleavage. The apex 

 adopts at once the continued development that is its characteristic. 

 Branching of various types follows in all but the simplest, to constitute 

 the complex shoot, while correlative basal branching gives the root-system 

 that fixes the non-motile body in the soil. The scheme of growth and 

 branching thus started is theoretically open to unlimited increase, and the 

 initiation of new parts is in point of number on a geometrical scale. This 

 is suitable enough for organisms able to accumulate material, as plants do ; 

 indeed, the elaboration of the vegetative system will enhance its powers 

 of self-nutrition, so far as the parts become functional ; but this is never 

 fully realised beyond the earlier steps. 



The focus of all such development is the growing point, respectively of 

 root or shoot. Anyone who carefully dissects a suitable bud, peeling off 

 the successively smaller leaves, may finally see with the naked eye or with 

 a simple lens a pearly cone of semi-transparent tissue at the tip of the 

 stem. This is the growing point itself, which possesses theoretically 

 unlimited formative power. It is like a permanent sector of the original 

 embryo that is fed continually from the mature tissues below, and as 

 continually forms fresh tissues at the tip. But as the tip advances, 

 lateral swellings of the surface appear in due order, which are new leaves 

 and buds. Various attempts have been made to link the genesis of these 

 outgrowths of the radial shoot with the outer world as regards their 

 position and number. But we have it as the latest authoritative statement 



