2l8 THE SCOTTISH BOTANICAL REVIEW 



Amongst Microspermae the Burmanniacese exhibit an affinity with 

 Liliiflorae. 



Thus far we have reviewed the results attained by the study of the 

 systematist. Let us see what morphology and embryology, with some 

 ecological facts, have to tell us. 



The opinion expressed by Schimper and Schenk in their text-book 

 of Palseobotany ^ largely coincides with the decision arrived at by 

 some of those who have based their researches upon the facts of 

 morphology or embryology. They consider that dicotyledons are 

 the older race. They remark upon the late appearance of mono- 

 cotyledons and their rare occurrence as fossils. They consider the 

 stem-structure proves that monocotyledons are the higher group. 

 It is pointed out that the dicotylous type of stem-structure is found 

 in fossil vascular Cryptogams and Gymnosperms. The simple floral 

 structure is thought to point to a group in process of evolution. 



Dr. W. C. Worsdell ^ holds the view that dicotyledons are derived 

 from monocotyledons, that the cotyledon is always terminal, and 

 that the stem-structure is not due to reduction but is primitive. He 

 regards the fruiting stem and petiole as alone able to unfold the true 

 ontogeny of the individual whereby the stages in the race-history 

 may be made out. Dr. Worsdell's latest view is that monocotyledons 

 and dicotyledons are variants of one form and that there is only otie 

 cotyledon. He has found a similar stem-structure of scattered 

 bundles in about thirty orders of dicotyledons, and considers the 

 dicotylar vascular system derived from the monocotylous. Many 

 other characters also are correlated with it. 



In Jungermannieae {cf. PI. II. fig. 3, part i. p. 180) the seta is 

 derived from the two epibasal quadrants, and it is considered that 

 the cotyledon is homologous with it, and terminal. It arises before 

 other organs, bearing out the sporogonial or phyton theory of the 

 plant, but not the lateral appendage view. If their development 

 is similar, then the single cotyledon has dichotomised to form two ; 

 and the plumule is then lateral to both cotyledons, and between 

 the two. And the bifid cotyledon is primarily terminal. " The 

 actual ontogenetically terminal position of the plumules is a 

 secondary adaptation," and in some plants, e.g. in palms, "it 

 becomes enclosed in the basal sheathing petiole of a single tubular 

 cotyledon, which is terminal to the hypocotyl." 



In the moss the seta is terminal. If we regard the cotyledon as 

 homologous and the monocotylous embyro an index of the history 

 of the leafy angiosperm, we have a succession of shoots arising, the 

 second like the first, and so on, till a terminal apex or growing point 

 is formed upon the axis thus produced by sympodial arrangement. 

 This monopodial axis with apparent lateral appendages is purely 

 illusory, and "we need to entirely amend our artificial conception 



1 1891, p. 348. 



'■^ Vide "A Study of the Vascular System in certain Orders of the Ranales," 

 " Ann. Bot.," Oct. 1908, p. 651 et seqq. 



