INDEPENDENT ORIGIN OF PARTS 



183 







than has often been assumed, and comparative arguments based on 

 embryological facts must be used with the greatest caution. 



The independence of origin of the separate parts thus seen in some 

 degree in the embryo calls for further consideration, since it is shown also 

 elsewhere than in the normal embryo, and it will affect in some degree 

 the conception of the nature of the parts of the plant. It is a common 

 experience in the plant at large that roots may arise independently of 

 other parts : frequently their occurrence is irregular both in number and 

 position, and this finds its illustration in almost all the large groups of 

 plants. Goebel l quotes examples of " free-living " roots, which do not 

 spring from a shoot at all, in Pyrola and Monotropa : he regards these 

 as derived from the normal in accordance with the saprophytic mode of 

 life of these plants. A very peculiar illustration of the detachment of origin 

 of roots is shown in the 

 abnormal cases of apogamy 

 described by Lang (Fig. 

 93) ; for here numerous 

 roots were formed inde- 

 pendently of any other 

 parts of the sporophyte ; 

 thus the idea of detach- 

 ment of the root is already 

 a familiar one. On the 

 other hand, the current 

 conception of the leaf is 

 of a part in close genetic 

 connection with the axis : 

 but this also has been 

 shown by Goebel to be 

 open to exceptions. He 

 describes cases of free- 

 living leaves. 2 The old 



morphological dogma asserted that a leaf could only arise out of the 

 vegetative point of a shoot ; but Goebel accepts the facts disclosed in 

 Lem/ia and Utriadaria, as well as the condition of the embryo in many 

 Monocotyledons, as overthrowing this dogma. In the latter case the 

 cotyledon arises without any vegetative point of an axis being visible. He 

 also quotes the case of Adiantum Edgeworthi, a Fern which produces buds 

 at each leaf-tip. 3 This case I regard as being important for comparison 

 with the condition seen in embryos ; for according to Goebel's description 

 and drawings (Fig. 94), the first leaf of the new bud arises not from the 



1 Organography, p. 234. - L.c., p. 235. 



3 L.i'., p. 241. See also Kupper, flora, 1906, p. 337, who found that in Adiantnm- 

 species three, and in Aiitimia rotundifolia even six leaves originated before the stem-apex 

 was defined. 



FIG. 93. 



^Scolopendriiim vnlgare. Prothallus from the branched cylindrical 

 process of which ten roots arose : eight of these are visible in the 

 drawing. X about 6. fAfter Lang.) 



