io GENERAL DIFFERENTIATION OF THE PLANT-BODY 



The inflorescences of Nidularium splendens, one of the Bromeliaceae, 

 are surrounded by a number of beautiful red 'bract-leaves,' which differ 

 from one another, and which make a showy attraction-apparatus. The 

 lowermost are quite like the ordinary foliage-leaves, except that their 

 basal part is red. In succeeding leaves the red portion gradually increases 

 until, in the uppermost, the entire leaf from base to apex is so coloured. 

 We may state this otherwise by saying that the transformation, which 

 here appears in the red colouration, commences sometimes earlier, 

 sometimes later, in the development of the primordium of the foliage- 

 leaf. The basal portion is that which matures latest in the development 

 of a leaf, and consequently when the transformation commences relatively 

 late the basal portion only is affected, the other parts are normal x . 

 In other Bromeliaceae, as, for example, Bilbergia, the passage from 

 foliage-leaves to bract-leaves is abrupt, yet the transformation itself 

 remains the same. Similar examples may be found in many plants 

 producing tendrils. In such tendrillous Fumariaceae as Corydalis clavi- 

 culata we find in the successive leaves of the seedling all transitions 

 from ordinary foliage-leaves which have not tendrils to those with 

 tendrils ; the stalks of the upper leaflets gradually elongate whilst their 

 blades correspondingly diminish until typical flagelliform tendrils are 

 produced. In Cobaea scandens, a tendrillous plant of the Polemoniaceae, 

 the transition from leaves without tendrils to leaves with tendrils is 

 on the other hand a sudden one ; but the developmental history of the 

 tendrils here shows 2 that they arise in quite the same way as is so 

 easily observable in the seedling plant of Corydalis claviculata the 

 tendrils themselves are greatly elongated leaf-petioles gifted with a 

 special sensitiveness, and the blades of the leaflets are visible as small 

 papillae at their terminations. We do not however find in all tendrils 

 the transformation of the primordium of the foliage-leaf taking the 

 course we have described. The ivhole leaf-primordium may be concerned 

 in the formation of the flagelliform tendril. The history of development 

 of the first tendrils of Benincasa cerifera, one of the Cucurbitaceae, 

 for example, shows us that a leaf-blade is distinctly laid down upon 

 them, but the whole leaf instead of developing into a flat expansion 

 elongates into a long filiform tendril ; this is not the case in subsequent 

 leaves. Numerous other examples will be given in the special part of 

 this book. 



One of the weightiest facts of the organography of plants is, in my 

 opinion, the indication that there is a traceable and direct developmental 



1 Eranthemum nervosum, a plant often cultivated in Botanic Gardens, shows a like condition of 

 the bract-leaves. 



' 2 Goebel, Vergleichende Entwicklungsgeschichte der Pflanzenorgane, p. 431. Compare also 

 A. Mann, 'Was bedeutet Metamorphose in der Botanik?' Inaug. Dissertation. Munich, 1894. 



