216 



the trutli of the Cdiiinionly nirule statement that many i)lants ean- 

 iiot he propagated by ciUlings. In the course of the lecture it 

 is made evident that in the light of modern investigation this 

 statement is nnjnstihed. Two remarkal)le cases are cited early 

 by way of illustration : one being the case of a species of Gyi> 

 sophila. which was formerly believed to he unresponsive to vege- 

 tative propagation., hut which had Ijeen shown by the author to 

 be easily reproduced by internodal cuttings. The second ca.se con- 

 cerned a plant of great importance in the trojiics — the bamboo — 

 which until recently had been considered only sexually repro- 

 ducible. I'rofessor lialfour, however, has sliowii the 1)amhoo to 

 be readily increa'^ed by cuttings. 



Proceeding next to general considerations of the mo.st interest- 

 ing nature concerning plants as individual organisms, it is pointed 

 out that a plant, unHke one of the higher animals is not. strictly 

 speaking", one incHvidual. It is a colonial organization. "A plant 

 is composed of a sheet of protoplasm (living substance) stretched 

 over a skeleton." A limb of a plant can he removed and another 

 will grow to replace it; if the limb of an animal be removed, 

 only mutilation can result. A plant is therefore potential]}' im- 

 mortal. 



Two common instances of vegetative reproduction in nature 

 were next cited — those of the iris and the strav\'herr\-. 'l"he for- 

 mer plant creeps along under the .soil forming new additions to 

 its body: in fact it is rui accident if the plant does not continue 

 to live for ever. In the case of the latter example, tiie plant 

 extends itself hy runners — ^by the formation of roots near ihc 

 terminal hud at the end of the pro.strate ofifshoot. 



Consideration of these two cases shows that the necessary con- 

 ditions for reproduction are (a) that the young buds whicli give 

 rise to the new .shoot must receive ample food-supply from the 

 parent plant until it has rooted itself; (b) that there be water to 

 stimulate root development. These two facts are of primary 

 im]:)ortance. 



After referring to the advantages that accrue to gardeners 

 from the presence of the bulblets, conns and the like amcMigst 

 nionocotyledonous plants, the author ])roceeded to the im])ortant 

 subject of callus formation in relaticMi to vegetative ])ro]xigation. 

 The growth of callus consists in the formation of a mass of living 

 cells under the stimulus of wounding. \n an ordinary <hcotyle- 

 donous stem or root it may take origin in the ])ith. in the medul- 

 lary ravs. in the cortex, or in the active wood cambium, and it 

 forms iol)ulated jirojecting masses at the ]K)int where it occiu's. 

 Callus more rarelv forms in monocotyledoncnis i^lants — these are 

 content to heal wounrls by a cork covering only ; when it does 

 appear, however, it arises from the cortex of the stem. Callus 

 formation is a mark of the colonial organization of the ])lant 

 already referred to. it is associated with the formation of adven- 

 titious roots. 



