154 DIFFERENCE OF ORGANS AT DEVELOPMENT STAGES 



for controlling transpiration especially is much less developed, as is to be expected 

 in plants growing under the protection of others. 



2. Larix. The juvenile form in this genus in its first, and occasionally also 

 in its second year, shows a difference from the adult, inasmuch as the leaves 

 persist during the winter as they do in species of the nearly allied genus Cedrus 

 and in Pinus, whilst on the ordinary shoots they are deciduous. 



3. Cupressineae. The formation of leaves in this group is very variable even 

 within one genus. Juniperus communis for example has the typical form of leaf of 

 the needle-leaved trees, namely, spreading needles. In Juniperus virginiana, species 

 of Cupressus, of Callitris, of Chamaecyparis, and of Thuya, the leaves of the mature 

 shoots are in great part ' concrescent ' by their upper side with the upper side of 

 the shoot ; and the needle-leaves are restricted to the juvenile form. In male 

 plants of Juniperus chinensis however twigs bearing needle-like leaves often appear 

 upon old plants l , the flowers however usually arise on the twigs which have 

 adpressed scale-like leaves, although I have occasionally found them in the axil 

 of needle-leaves. Twigs with needle-leaves which I used as cuttings seven years 

 ago have now grown into bushes nearly 2 m. high, and these have retained 

 their form of leaf but will likely produce later twigs with adpressed leaves. The 

 juvenile stage in all the genera mentioned has spreading leaves and the plant can 

 be fixed in this form, growing into high stems with quite a different appearance 

 from that of the normally developed plants of the same species 2 . Such plants do 

 not usually produce flowers and yet this may occasionally take place. I have else- 

 where 8 referred to the instances of this which are described in the literature, and 

 I have myself subsequently seen an example at the Lago di Garda. The juvenile 

 forms of these plants (and the same is the case in Pinus) must undoubtedly be 

 considered as the more primitive and we have thus been able to revive to 

 a certain degree their stem-form ! That the fixed juvenile forms retain their con- 

 figuration and are usually unable to produce sexual organs, although external 

 conditions are quite favourable for this, when they have attained an age and 

 a size at which the normal plants are and have been for long sexually mature, 

 is an extremely interesting feature of the development. Between juvenile forms 

 and adult forms there are naturally transitions and these can be fixed, but under 

 favourable conditions pass over more or less quickly into the adult form. 



It is probable, especially from the analogy with cases which will be mentioned 

 immediately, that in the Coniferae which have been described above, the duration 

 of the juvenile form of uninjured individuals can be prolonged by definite external 

 influences. The experience of different breeders has led Beyerinck to say 4 that 

 'all circumstances which prejudice nutrition favour the retention of the juvenile 

 character/ and consequently the juvenile form is retained longer when plants are 



1 See Goebel, Pflanzenbiologische Schilderungen, i. Fig. n. 



2 These juvenile forms^ are known in gardens as species of Retinispora, and gardeners have 

 maintained that they remain small and do not reach a great age. This is not however every- 

 where true (see my papers cited at the beginning of this section) ; and yet we need not be 

 surprised if plants produced from cuttings have a root-system less developed than the normal, 

 and if the leaves of the juvenile form being softer are less resistant than the adult ones. 



3 Goebel, in Flora, 1889, p. 36. 4 Beyerinck in Botan. Zeitung, 1890, p. 539. 



