282 BOTANY PART i 



while "rosette plants," in which the leaves are separated by hardly 

 recognisable internodes, stand in striking contrast to them. 



2. The Phases of Growth 



In the simplest plants, such as the lower Algae, Fungi, or Bacteria, 

 development consists merely in growth of the cell followed by cell 

 division. These cases have been sufficiently dealt with in the morpho- 

 logical section. In more complex plants growth and division of cells 

 are also found, but these processes appear subordinated to the growth 

 of the whole. Three distinct processes can be distinguished in this, 

 though they are not always separated in time. These are the stage of 

 FORMATION OF EMBRYONIC ORGANS, that of ELONGATION, and the stage 

 of INTERNAL DEVELOPMENT ( 54 ). 



(a) Embryonic Rudiments. The embryonic growth takes place 

 normally at the growing 1 points, and new growing points arise as a 

 rule directly from the latter. Only in the case of roots is the forma- 

 tion of the growing points of lateral branches somewhat delayed and 

 takes place from remains of the growing point which have retained 

 the embryonic character. The main features of the formation of 

 organs at the growing points have been dealt with in the section on 

 Morphology. SYMMETRY and POLARITY have been considered on 

 p. 74 ff.; these are often manifested even at the growing point. The 

 contrast of base and apex which constitutes polarity is determined in 

 the egg-cell in higher plants, and is as a rule maintained when once 

 established. It must be pointed out here that all growing points do 

 not arise from pre-existing similar ones. Development of the plant 

 can proceed by restitution as well as by the normal organogeny. 



By Restitution ( 55 ) is understood the new formation of organs 

 which as a rule follows the mutilation of a plant, and can take place 

 in situations where no active growth would have been manifested in 

 an uninjured plant. The types of restitution may be distinguished 

 as regeneration and reparation. 



REPARATION is when the lost organ is again formed from the 

 wounded surface. This kind of restitution, though not uncommon 

 in lower plants such as Algae and Fungi, is of very restricted occurrence 

 in the higher plants. Only tissues that are meristematic or embryonic, 

 and by no means all of these, are capable of reparation. It is most 

 frequently seen in the growing point of roots ; when the tip is removed 

 by a transverse cut, if this is not more 'than 0'5 mm. from the tip, 

 it may be again formed. A longitudinally-split root-tip tends to com- 

 pletion by reparation, so that a root thus treated may obtain two 

 growing points. True reparations do not occur at the growing points 

 of shoots ; they are rare in the case of leaf-primordia. 



REGENERATION, on the other hand, is wide-spread among plants. 

 In this case an organ which has been lost is replaced either by the 



