1 68 DIFFERENCE OF ORGANS AT DEVELOPMENT STAGES 



clearly that the primary leaves take origin through the same processes. 

 In Carmichaelia Engsii simple foliage-leaves alone appeared on the seed- 

 ling plant, and these in many examples were reduced to unstalked small 

 scales, so that we have here in one genus the transition from heteroblastic 

 to homoblastic germination. 



Bossiaea rufa exhibits the same kind of germination as Carmichaelia 

 stricta. The chief axis of the seedling produces a number of stalked 

 oval leaves and is not broadened out. It is subsequently arrested, whilst 

 out of the axils of the cotyledons and beneath them shoots develop 

 which gradually become phyllocladcs. On these flat shoots the small 

 pointed stipules only of the leaves remain, the primordium of the blade 

 is arrested T . Other species of Bossiaea possess also flat twigs with well- 

 formed leaves, for example, B. heterophylla, or cylindric twigs with foliage 

 leaves, for example, B. microphylla 2 . We thus find in one genus all 

 stages of transition. 



Ulex europaeus, in which the leaves in the mature plant are transformed 

 into thorns, possesses on the seedling plant after its first primary leaves 

 trifoliate foliage-leaves like other GenLsteae. The lateral leaflets on the 

 leaves standing higher up on the stem gradually diminish in size and at 

 last do not develop. The leaf now becomes simple and linear, is 

 gradually transformed into a thorn, and at the same time the twigs also 

 develop as thorns. 



Colletia likewise deserves notice here ". The species of Colletia form 

 spinose shrubs and the older plants bear small deciduous leaves. In 

 C. cruciata the thorns, which are the lateral shoots, are strongly flattened. 

 The seedling plants of all the species of Colletia known to me arc 

 constructed exactly alike ; they have cylindric shoot-axes with well- 

 developed foliage-leaves and the flattening of the shoot-axes in C. cruciata 

 only takes place later. The configuration of the seedling plant proves 

 itself here also to be a primary character. 



Cacteae. The behaviour of Colletia cruciata finds an analogue in 

 that of many Cacteae. The formation of foliage-leaves does not take 

 place in the seedlings of the Cacteae, the leaves are here transformed 

 into scales or spines, but the shoot-axes frequently show more primitive 

 relationships of configuration than appear in the older plants. We may 

 consider the following construction of the vegetative body as ' typical ' 

 for the majority of the leafless Cacteae fleshy shoots invested by chloro- 

 phyll-tissue and bearing tufts of spines in the axil of small scale-like 

 leaves. The spines are transformed leaves which arise upon very much 



1 Hildebrand's statement that 'there is no trace of the leaf-blade ' is certainly wrong. 



2 Askenasy Botanisch-Morphologische Studien. Frankfurt a. M. 1872, p. 4. 



3 For a Figure see Goebel, PflanEenbiologische Schilderungen, i. Fig. 8. 



