84 MORPHOLOGY OF SPECIES 



months, and was well-supplied with water. The seedling to start 

 with was two centimetres long. The main axis continued growing 

 and developed first of all eight more trifoliate leaves, then six di- 

 foliate ones, and then a number of thin, linear, lanceolate leaves, 

 with only a slight rudiment of a spine at the apex. The stem 

 remained thin, and the leaves never became stiff or spiny. This 

 main axis grew to about twenty centimetres long while it was 

 under my observation. In the axils of the upper leaves, spiny 

 branches were produced, but the spines never became prominent, 

 whilst the lateral leaves borne upon them were generally well 

 developed, and in many cases no spine was formed at all. Three 

 of the lower trifoliate leaves developed branches which were 

 respectively 5, 6, and 7J cm. long. Neither of them had termin- 

 ated their growth by a spine, and on all of them the leaves 

 remained thin, flexible, and only very feebly spined. In the axils 

 of only a few of these leaves were any spiny branches produced, 

 and these were only very rudimentary, and in no case was the 

 spine developed. The following details of one of these branches 

 may be interesting : — 



Leaves i to 9. — No branches at all in their axils. 

 „ 10 and II. — The two lateral leaves only of the 



spiny branches developed. 

 „ 12 and 13. — A small bud only in their axils. 

 „ 14 and 15. —Two lateral leaves only, no spine. 

 „ 16 to 27. — Two lateral leaves only slightly 



spiny, but no main spine. 



Under normal conditions, as I was careful to observe, such a 

 seedling would have developed a very definite spiny structure 

 during the few months I had it under observation. The seedling 

 was ultimately killed by an exposure to a couple of months' 

 drought, but the observations are sufficient to show that a good 

 supply of water and non-exposure to cold tends to retard the 

 development of the spiny nature of the plant, not only by 

 reducing the stiff spiny nature of the leaves, but also by reducing 

 the stiff spiny nature of the stem, and allowing a much greater 

 development of length at the expense of sturdiness and the 

 development of leaves which are capable of fulfilling the leaf 



