96 Root-Cuttings and Chimaeras II 



Spiraea ulmaria. 



A variegated form has stems, petioles, and central parts of the leaf- 

 lets devoid of chlorophyll (PI. XIV, fig. 2), and of a whitish yellow colour. 

 Ordinary green plants are perfectly fertile on both male and female sides, 

 but this variegated plant is quite sterile, forming no seeds or pollen, 

 A few ill-formed carpels have been found on it, but the seeds they con- 

 tained were aborted and did not germinate. The condition is closely 

 reminiscent of the zonal Pelargonium, "Freak of Nature," mentioned in 

 Jour. Gen. 1919, viii. p. 97, note, which has green borders to leaves and 

 stipules and is totally sterile on both sides. The extraordinary feature 

 of that plant is that the green, white, and green-over- white shoots which 

 Freak of Nature often produces are perfectly fertile. The variegated 

 Spiraea has not hitherto produced any shoots other than those described. 

 From its roots it readily gives rise to adventitious buds, and all leaves 

 borne by them are albino, quite destitute of chlorophyll, like the stalks 

 and petioles. 



In my previous article on root-cuttings I spoke of the dissimilar forms 

 which arise as being in all probability included as "cores" within a 

 cortex of the ostensible type. The whole plant is thus regarded as a 

 periclinal chimaera, one variety enclosing another, and this enclosed form 

 may be expected to come out whenever the plant makes an adventitious 

 bud by endogenous growth. Though this view is presumably correct in 

 most cases the distribution seen in the variegated Spiraea and Freak of 

 Nature show that other possibilities must be remembered. For in these 

 plants the white tissue is not covered in, but extends through the whole 

 of the internodes, and doubtless the root also. The growing point alone 

 carries up with it the power of making green tissue. In such plants as 

 the Bouvardia or Pelargoniums which give dissimilar root-cuttings the 

 two kinds of tissue are not recognizably distinct in the plant until they 

 flower, and though perhaps unlikely, it is not impossible that the kind 

 which arises by adventitious buds may really provide the whole of the 

 root and perhaps the internodal regions. Many herbaceous variegated 

 plants arranged periclinally are liable to give shoots composed entirely 

 of either their external or their internal constituents. Such shoots with 

 special frequency arise near the base of the plant, i.e. just above the level 

 at which the stem was divided in propagation. Though their mode of 

 origin is not always easy to decide, it must be supposed that they are 

 generally produced by adventitious buds. These evidently are not always 



