THE SNAP-DRAGON FAMILY 375 



He has found, that in several cases at least, the seedling 

 passes through a stage with large leaves, unlike those of the 

 mature form. The development of Veronica tetrasticha* may 

 be taken as an example. It is a beautiful little sub-alpine 

 plant, with tetrangular stem and cupressoid leaves. Dr. 

 Cockayne collected seeds of it from plants growing on shingle 

 slips on the Craigieburn Mountains. They were planted, and 

 found to be slow of germination, and the remarkable conclusion 

 was come to, that, " between the juvenile and mature plants, 

 so far as observed, there is no resemblance." The adult plant 

 has minute, overlapping, dark-green leaves, appressed to the 

 stem, narrowly triangular in shape, with broad sheathing bases 

 that meet round the stem. They are fleshy, concave on the 

 upper surface, and flat on the lower, and often bear a row of 

 marginal hairs. On the other hand, the first leaves produced 

 subsequently to the cotyledons, are spathulate, with or without 

 petioles, " pale-green above and purplish beneath, covered above 

 and beneath with erect, stout-hooked, white hairs, with hooks 

 turned upwards towards the apex of the leaves." The base 

 only of the leaf is appressed to the stem, the rest of it being 

 spreading, with the apex curving downwards. The leaves, 

 though succulent, are scarcely fleshy. So far as the other 

 whip-cord veronicas have been observed, similar differences 

 between the young and mature forms have been noticed. 

 Perhaps the most remarkable result of Dr. Cockayne's 

 researches, was the proof that the seedling form remains 

 permanent, so long as the plant is kept in a warm moist 

 atmosphere. 



Various theories have been put forward to explain the 

 depauperated leaf forms of these veronicas. Prof. Henslow 

 compares them to Tamarix, Thuja and CupressusJ, and 

 says, with regard to the origin of all such plants, that : " such 

 forms are due to precisely the same causes ; the same or 

 homologous organs put on precisely the same morphological 



*Trans XXXI., p. 377. tThe Origin of Plant Structures, p. 108. 



