828 REPOBT— 1901. 



cotyledon.'' Tlie rupture of the seed and the placing of the plumule along wilh 

 the primaiy root — for the axis of the corin does not elongate between them — are 

 the work of the base of the suctorial portion of the corm. 



The whole arrangement in Mouocotyledones is in marked contrast with that of 

 the Dicotyledones. Instead of the free axial elongation begun in the protocorm 

 and continued upwards aud downwai'ds in the epicotyl and primary root, there is 

 limited axial growth of the protocorm with lateral outgrowth of the plumular bud 

 aud arrest of the primary root. These differences in the protocorm are, I think, 

 primary, and they point to independent origins of the two groups. The advan- 

 tage lies, as I have said, with the Dicotyledones, and we find that the features of 

 development of the protocorm are continued in the adult. There is a marked con- 

 trast between the free internodal growth of the shoots of Dicotyledones with their 

 copious root-system and the contracted stem-growth and the arrested root-system 

 in Monocotyledoues. It.is interesting to note further how the monocotylous type 

 has developed so largely upon restricted lines in the v.'ay of short rhizomatous, 

 often tuberous, growth, whilst the dicotylous gives us the characteristic growth- 

 form tree. 



When we compare the tree-type of the Dicotyledones with that of the Mouo- 

 cotyledones we see at once the feature I refer to in the adult, which has given the 

 advantage to the dicotylous type in respect of its water-supply. In Dicotyledones 

 we have a much-branched stem ending with numerous shoots with long in'ternodes 

 and small apices, and bearing many small leaves which are mainly deciduous. In 

 the monocotylous tree, of which we may take the palm as a type, there is a 

 straight stem with short internodes, a large apex bearing few large leaves not 

 often renewed ; if there bo branching it takes more or less the form of a fork. 

 The whole of this external configuration bears relationship to the internal structure. 

 In the Dicotyledon the open bmidles of the central vascular system provide 

 through their cambium for a continued increase of the water-carrying system and 

 medullary rays, wliich, although it is to many a heresy, I hold to have profound 

 influence upon the movement of water in trees. Tlie buttressing of the branches 

 is also secured, and thus is rendered possible a large assimilating area made up of 

 a vast number of small individual surfaces, each one of which can be readily 

 thi-own off. In the Mouocotyledones, on the other hand, the distribution of a 

 large number of closed vascular bundles in a matrix without a cambium involves 

 the provision of a broad terminal cone, gives no support, outside interstitial 

 growth, to lateral branches, which are consequently when developed placed 

 so as to give an equipose, and the assimilating surface has to be concentrated in a 

 few large leaves. The possession of cambium has enabled the Dicotyledones to 

 meet in a mtich better way the requirements of water-supply and strength in 

 correlation with feeding. 



The general uniformity and effectiveness of the scheme of cambial growth is a 

 remarkable feature in the dicotylous type ; but there is still a wide field of investi- 



' I use the term purely as an objective designation, and in the original meaning 

 of the suctorial organ in the embryo. This terminal cotyledon in the Jlonocotyle- 

 dones is not a leaf nor the homologue of the lateral cotjledones in the Dicotyledones. 

 The ' traceable and direct developmental history in the formation ' of the two organs 

 is clear, aud they are not alike. To those who hold the contrary view a terminal leaf 

 is no obstacle. I think, however, the question of lateral or terminal is of importance 

 in organography. The ' sympodial leaf-from-leaf evolution,' described in tlie first 

 epicotylar stages of Juncus, Pistia, and other plants, demands examination with the 

 aid of modern methods. All cases of vegetative organs in which the distinctions 

 between organs are said to brealc down arc worthy of being looked at in the light 

 of their relation to their nutritive environment. Rovyr nutrition afEects plant-form 

 we do not yet understand. Its effects are familiar, both in vegetative and repro- 

 ductive organs. The grosser cases, in parasites, show in the extremes an abolition 

 of most of the landmarks of morphology — ' the whole scheme of formation of organs 

 is jumbled.' Heterotrophic ' jumbles ' do not, however, deny the ordinary morpho- 

 logical categories. Pseudo-terminal reproductive organs are to be expected under the 

 cessation of growth with which their development is concurrent. 



