164 DIFFERENCE OF ORGANS AT DEVELOPMENT STAGES 



In the special part of this work I shall treat of the Cucurbitaceae 

 which bear tendrils and I will only mention here that, as I have elsewhere 

 shown 1 , the formation of simple tendrils characteristic of the seedling may 

 appear in adult plants if they are badly nourished. 



B. AQUATIC AND MARSH PLANTS. 



Only a few of these are briefly referred to here because I have so 

 fully dealt with many of them elsewhere 2 . 



The primary leaves of all the Sarraceniaceae are essentially alike in 

 their configuration whilst the later ones are often markedly different from 

 one another. The features exhibited by the seedlings of Utricularia are 

 of special importance because they show a complete conformity between 

 the whole construction of the land-species and the water-species which 

 subsequently are widely different from one another. An adaptation which 

 renders difficult the overturning of the embryo-plants is visible in the 

 configuration of the peltate primary leaves of Salvinia and the turbinate 

 ones of Azolla 3 . The peculiar submerged primary leaves which appear 

 in many Nymphaeaceae must be considered as arrested formations ; the 

 floating leaves arise later, but their formation may be entirely suppressed 

 in Nuphar if the conditions are unfavourable, so that the plant persistently 

 forms leaves which correspond with those of the seedling. 



The behaviour of some monocotyledonous plants has given occasion 

 for a different explanation. All of the Alismaceae, Pontederiaceae, and 

 Potamogetoneae which have been as yet examined, no matter how different 

 the adult form of their leaves may be, agree in the production in 

 germination of simple band-like leaves which were formerly erroneously 

 called phyllodes. By intermediate stages they pass into the higher form 

 of leaf which is provided with a stalk and blade. The primary form of leaf 

 is retained by individual species for a varying length of time ; for the 

 longest period by those which live more submerged. Amongst these, for 

 example Heteranthera zosteraefolia and Sagittaria natans, the higher form 

 of leaf only appears on the flowering plants and then only in a few leaves, 

 whilst numerous band-like leaves are present ; on the other hand these 

 band-like leaves are found in the species more adapted to a land-life only 

 as a stage of development rapidly passed over. Differences of this kind 

 are found even in species of the same genus, as a comparison of Sagittaria 

 natans and Sagittaria cordifolia shows, for in the latter species the primary 

 leaves play only a subordinate part. 



1 Goebel, Vergleichende Entwicklungsgeschichte der Pflanzenorgane, p. 240. 



= Goebel, Pflanzenbiologische Schilderungen, ii. Numerous figures will be found in this work. 



3 See Fig. 73 in my ' Pflanzenbiologische Schilderungen,' ii. 



