310 BOTANY PART I 



from them remain alive. Thus we see that every cell which has 

 lost its embryonic character dies after a longer or shorter time. 

 Though this cannot as a rule be prevented, we cannot say that the 

 death is necessary. It is because certain cells develop that others 

 die, and their death is a phenomenon of correlation. In plants that 

 are capable of restitution the removal of the growing point before 

 the permanent tissue has become too old leads to fully-grown cells, 

 which would normally die, becoming embryonic again and continuing 

 to live. 



The longevity of trees ( 73 ) having an historical interest isnaturally best known and 

 most celebrated, although, no doubt, the age of many other trees, still living, dates 

 back far beyond historical times. The celebrated Lime of Neustadt in Wurtemberg 

 is nearly 700 years old. Another Lime 257 m. in circumference had 815 annual 

 rings, and the age of a Yew in Braburn (Kent) which is 18 m. in circumference is 

 estimated at 2880 years. Sequoia gigantea, the giant tree of California, attains 

 according to H. MAYE, the age of 4000 years. An Adansonia at Cape Verde, whose 

 stem is 8-9 m. in diameter, and a Water Cypress (Taxodium mexicanum) near 

 Oaxaca, Mexico, are also well-known examples of old trees. The celebrated 

 Dragon tree of Orotava, which was overturned in a storm in 1868, and afterwards 

 destroyed by fire, must have been some 600 years old. Bryophytes also may 

 attain a great age ; the apically-growing mosses of the calcified Gymnostomum 

 clumps, and the stems of the Sphagnaceae, metre-deep in a peat-bog, must 

 certainly continue to live for many centuries. 



E. Reproduction 



Cell division, especially when the two resulting cells separate, can 

 be regarded as a process of reproduction. In more complex organisms 

 also vegetative growth often passes gradually into reproduction. 

 Only those forms of reproduction require special consideration in 

 which special organs are formed (reproductive organs, germs) which 

 separate from the parent plant and, at the expense of a supply of 

 reserve material, commence a new life. In this way young organisms 

 originate which then repeat the development of the parent organism, 

 its gradual increase in strength, and its later decay. Often these 

 reproductive organs have the further duty of carrying the organism 

 over a period of cold or drought ; they thus constitute a resting 

 stage. With favourable conditions their growth recommences, they 

 germinate. 



Reproduction is concerned, however, .not merely with the continua- 

 tion of the parent organism, but at the same time with an increase 

 in the number of individuals (p. 192). For the continuance of the 

 species it is not only necessary that numerous germs should be 

 produced, but that they should be widely distributed ; as a rule there 

 will be no room for new individuals to grow in the place where the 

 plant which bears the seeds is growing. 



