218 The Palaeontological Record. II. Plants 



those of the palaeontologist ; still there are certain important points 

 involved, on which the palaeontological record appears to bear. 



One of these points is the supposed distinction between morpho- 

 logical and adaptive characters, on which Nageli, in particular, laid 

 so much stress. The question is a difficult one ; it was discussed by 

 Darwin \ who, while showing that the apparent distinction is in part 

 to be explained by our imperfect knowledge of function, recognised 

 the existence of important morphological characters which are not 

 adaptations. The following passage expresses his conclusion. "Thus, 

 as I am inclined to believe, morphological differences, which we 

 consider as important — such as the arrangement of the leaves, the 

 divisions of the flower or of the ovarium, the position of the ovules, 

 etc. — first appeared in many cases as fluctuating variations, which 

 sooner or later became constant through the nature of the organism 

 and of the surrounding conditions, as well as through the inter- 

 crossing of distinct individuals, but not through natural selection; 

 for as these morphological characters do not affect the welfare of the 

 species, any slight deviations in them could not have been governed 

 or accumulated through this latter agency^" 



This is a sufficiently liberal concession ; Nageli, however, went 

 much further when he said: "I do not know among plants a morpho- 

 logical modification which can be explained on utilitarian principles^" 

 If this were true the field of Natural Selection would be so seriously 

 restricted, as to leave the theory only a very limited importance. 



It can be shown, as the writer believes, that many typical 

 "morphological characters," on which the distinction between great 

 classes of plants is based, were adaptive in origin, and even that 

 their constancy is due to their functional importance. Only one 

 or two cases will be mentioned, where the fossil evidence affects the 

 question. 



The pollen-tube is one of the most important morphological 

 characters of the Spermophyta as now existing — in fact the name 

 Siphonogama is used by Engler in his classification, as expressing 

 a peculiarly constant character of the Seed-plants. Yet the pollen- 

 tube is a manifest adaptation, following on the adoption of the 

 seed-habit, and serving first to bring the spermatozoids with greater 

 precision to their goal, and ultimately to relieve them of the necessity 

 for independent movement. The pollen-tube is constant because it 

 has proved to be indispensable. 



In the Palaeozoic Seed-plants there are a number of instances 

 in which the pollen-grains, contained in the pollen-chamber of a 

 seed, are so beautifully preserved that the presence of a group of 



» Origin of Species (6th edit.), pp. 170—176. * Ibid. p. 176. 



3 See More Letters, Vol. ii. p. 376 (footnote). 



