A PLANT WITH UNDERGROUND SPINES 



PLANTS and animals both have 

 developed spines as a means of 

 protection against their enemies 

 but it is rare indeed to find a 

 plant with the spines below ground. 

 The all too common sawbrier (Smilax 

 Bonanox L.) of the southern states and 

 northern Mexico is one of the few plants 

 thus provided (Fig. 10). The stems 

 above ground are spiny to keep off 

 grazing animals but the underground 

 starchy tubers are armored densely 

 with spines apparently developed as a 

 protection against peccaries — the wild 

 pigs still found in the southwest. The 

 sawbrier is undoubtedly spreading rap- 

 idly northward fromi Mexico and is now 

 beyond the original range of the wild 

 pigs but its armor comes into use against 

 the ravages of the domesticated hog of 

 the old world. 



It is an interesting thing that the 



greenbriers of this region are very well 

 fitted to survive against most of the 

 adverse conditions imposed by civiliza- 

 tion. They are all geologically new- 

 comers in America and all actively 

 spreading — some from the south and 

 some from the east. Smilax hispida 

 came in from the northwest ages ago 

 and has now reached the Atlantic coast 

 where it is found in association with 5. 

 rotundijolia whose relatives are all 

 European. The invasion of the green- 

 briers will probably go on until they will 

 all spread over the whole region. 



The sawbrier {Smilax Bonanox) is 

 better fitted to survive than any of its 

 relatives who, while they have spines 

 above ground, rarely have any below 

 although they show enough traces of a 

 spiny cover to suggest the way in which 

 this interesting armor was evolved. 



What Determines Longevity? 



Under normal conditions, most com- 

 plex animals have a characteristic and 

 rather sharply defined duration of life. 

 But one celled animals, which reproduce 

 by fission, are apparently immortal 

 unless life is stopped by what may be 

 called an accident, for as the cell divides 

 in half, neither part may be called the 

 parent, and both halves will go on repro- 

 ducing. And by taking cuttings from a 

 plant, a part of the original may be kept 

 living indefinitely by repeated cuttings, 

 while the parent plant dies at the close 

 of its usual duration of life. Thus it 

 would appear that natural death is con- 

 nected only with organisms which are 

 composed of different organs which are 

 inseparable. 



Jacques Loeb and J. H. Northrop be- 

 gan experiments in 1908^ in an attempt 

 to find some of the causes which regu- 

 late the duration of life. Their work 

 was carried on with the fruit-fly, 

 Drosophila, which has a characteristic 

 duration for both the larval and adult 

 stages. It has already been definitely 

 proved that the termination of the first 



stage of a metamorphosis is deter- 

 mined by the production in the body of 

 certain chemical constituents not here- 

 tofore present. 



It is known that various life pro- 

 cesses have the same "temperature 

 coefficient" as chemical reactions — ■ 

 every increase of 10° C. in the tempera- 

 ture doubles the speed of the process (or 

 the reaction) . This is, naturally, if such 

 life-processes are themselves due to 

 chemical reactions. 



By breeding fruit flies at different 

 temperatures, Loeb and Northrop 

 seemed to find a similar temperature 

 coefficient. Every increase of 10 degrees 

 meant that the fiies bred at that tem- 

 perature reached the end of their lives 

 just twice as rapidl}^ as those bred in a 

 temperature 10 degrees cooler. Hence, 

 the authors think, it may be that lon- 

 gevity itself is determined by a chemical 

 reaction — -that normal death from old 

 age is due to the production in the sys- 

 tem of some poison which did not pre- 

 viously exist there. 



' Loeb, Jacques, and J. H. Northrop. What Determines the Duration of Life in Metazoa? 

 Proc. Nat. Acad. Sci., iii, pp. 382-386. May, 1917. 



569 



