376 BOTANY [CHAP. XI 



Letter 697 notes about this difficulty ; but I have hitherto slurred it 

 over. Nageli gives as instances the alternate and spiral 

 arrangement of leaves, and the arrangement of the cells in 

 the tissues. Would you not consider as a morphological 

 difference the trimerous, tetramerous, etc., divisions of flowers, 

 the ovules being erect or suspended, their attachment being 

 parietal or placental, and even the shape of the seed when 

 of no service to the plant. 



Now, I have thought, and want to show, that such differ- 

 ences follow in some unexplained manner from the growth 

 or development of plants which have passed through a long 

 series of adaptive changes. Anyhow, I want to show that 

 these differences do not support the idea of progressive devel- 

 opment. Cassini states that the ovaria on the circumference 

 and centre of Compos, flowers differ in essential characters, 

 and so do the seeds in sculpture. The seeds of Umbelliferae 

 in the same relative positions are ccelospermous and ortho- 

 spermous. There is a case given by Augt. St. Hilaire of an 

 erect and suspended ovule in the same ovarium, but perhaps 

 this hardly bears on the point. The summit flower, in Adoxa 

 and rue differ from the lower flowers. What is the difference in 

 flowers of the rue?, how is the ovarium, especially in the rue? 

 As Augt. St. Hilaire insists on the locularity of the ovarium 

 varying on the same plant in some of the Rutacese, such differ- 

 ences clo not speak, as it seems to me, in favour of progressive 

 development. Will you turn the subject in your mind, and 

 tell me any more facts. Difference in structure in flowers in 

 different parts of the same plant seems best to show that they 

 are the result of growth or position or amount of nutriment. 

 I have got your photograph 1 over my chimneypiece, and 



meanings given to the term morphological makes another difficulty. 

 Nageli cannot use it in the sense of " structural " -in which sense 

 it is often applied, since that would mean that no plant structures have 

 a utilitarian origin. The essence of morphology (in the better and more 

 precise sense) is descent ; thus we say that a pollen-grain is morpho- 

 logically a microspore. And this very example serves to show the 

 falseness of Nageli's view, since a pollen-grain is an adaptation to aerial 

 as opposed to aquatic fertilisation. In the $th edition of the Origin^ 

 1869, p. 151, Darwin discusses Nageli's essay, confining himself to the 

 simpler statement that there are many structural characters in plants to 

 which we cannot assign uses. See Vol. I., Letter 207. 

 1 A photograph by Mrs. Cameron. 



