SEASONAL DIMORPHISM OF CHAMAEPHYTES 219 



reduction to the regulation of their total water output during the prolonged 

 dry summer of the Mediterranean chmate. 



As seen from Table i the relative seasonal body reduction of the desert 

 plants examined was far higher than that of the Mediterranean ones. The 

 question which may arise is whether this difference is due to the effect of 

 the environment or to some internal characteristics in which the two 

 groups of plant differ from each other. 



The fact that the relative seasonal body reduction of the same species 

 was of similar magnitude for the two successive years examined, in spite 

 of the striking differences in the total rainfall between them, and that no 

 marked differences could be found in this respect between desert and 

 Mediterranean plants, supports the postulate that the differences in the 

 relative seasonal body reduction between the Mediterranean and desert 

 plants is in some respects, at least, due to certain inherent characters. 



Although no great differences between the values of the relative seasonal 

 body reduction for the years 1957 and 1958 could be found, the absolute 

 values of the seasonal body reduction in 1957, which was a better year, 

 were much higher than those in 1958 for the desert plants, but not for the 

 Mediterranean ones. These higher values were due to more extensive 

 growth in the spring of 1957, as seen from Table 3, affecting mainly the 

 number of dohchoblasts developed and their length. The fact that in the 

 Judaean hiUs no such differences between 1957 and 1958 were observed, 

 suggests that annual rainfall in the Judaean hiUs during the winter of 

 1957-58 was not a Umiting factor for growth of the Mediterranean plants. 



The question which one may put forward is whether the amount of 

 rainfall limiting spring growth is different for desert and Mediterranean 

 plants. 



If one considers the phenomenon of seasonal body reduction as partial 

 drought evasion (Orshan and Zand, 1961), one must admit that the 

 plasticity of the plant with regard to the extent of spring growth is more 

 extensive than that of the part of this growth which is being shed during 

 the summer. The absolute volume of the plant body which is shed during 

 the summer seems therefore to be more or less predetermined in the spring. 



The partial drought evasion of the desert chamaephytes, however, goes 

 one step further than that of the Mediterranean by some kind of radial 

 subdivision of the plant when only a sector of it remains ahve while the 

 rest dies back to the roots. During the next rainy season, the sector which 

 did remain alive grows into a whole plant (Ginsburg, 1961). 



This radial subdivision is achieved through different anatomical mecha- 

 nisms in various desert chamaephytes and there are some hints of its 



