DORSIVENTRAL SHOOTS. ANISOPHYLLY IN SPERMAPHYTA 107 



appears, and this is also a feature widely spread amongst dorsiventral 

 shoots (see Fig. 61). Whilst then in Lycopodium complanatum two 

 opposite leaf-rows of the four share in the constitution of the assimilating 

 surface, in Selaginella two leaf-rows adjacent to one another are devoted 

 to this purpose ; in the former a striking change of form, almost amounting 

 to abortion in the leaves of the row upon the shaded side, takes place, 

 in the latter the large leaves are displaced towards the illuminated side 

 whilst they are still in the condition of primordia at the vegetative point, 



FIG. 61. Selaginella haematodes. Transverse section through the apex ot a shoot. The obliquely-crossing 

 leaf-pairs are numbered in the succession of their age. The leaves upon the upper side are smaller than those 

 upon the under side. Leaves 8 and 9 are not entirely shown ; in the second and fifth leaf-pair the number 

 belonging to the under leaf has not been put in. 



and the two rows of smaller leaves adpressed to the shoot-axis take also 

 a part in the assimilation. 



From what has been said, namely 



1. In Selaginella sanguinolenta alone of its genus anisophylly is 



not constant but appears under the influence of external factors ; 



2. In many robust species of Selaginella the shoots are still isophyl- 



lous in their lower part ; 

 and further 



3. In etiolated shoots of Selaginella helvetica, as I have recently 



observed, anisophylly has not entirely disappeared but is only 



retarded l ; 



we may learn that in the ' habitually ' anisophyllous species of Selaginella 

 we have a phenomenon purely of adaptation brought about by light ; 

 the effect of the adaptation is however already visible in the relationships 

 of configuration at the vegetative point. We have also seen examples of 

 this in the lateral shoots (see page 95). 



D. SPERMAPHYTA 2 . 



Anisophylly occurs in different degrees in the same cycles of affinity, 

 and even in the same genus amongst higher plants, just as it does amongst 



1 See also Hofmeister, Allgemeine Morphologic, p. 626. 



2 See, in addition to the literature cited on page 100, Wiesner, Studien iiber die Anisophyllie 

 tropischer Gewachse, in Sitzungsber. d. Wiener Akad. d. Wissensch., ciii. Abt. i (1894) ; Hallier, 

 Neue und bemerkenswerte Pflanzen aus dem malaiisch-papuanischen Inselmeer, in Annales du Jard. 

 Bot. de Buitenzorg, xiii. p. 279. 



