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SCIENCE 



[N. S. Vol. XLII. No. 1092 



bryos of plants have given the key to doubt- 

 ful questions of phylogeny. What help do 

 they give us, for instance, in the algee or 

 the vascular cryptogams? The extension 

 of the idea of recapitulation to the succes- 

 sively formed regions of the seedling plant 

 requires critical examination; if admitted 

 it is at any rate something different from 

 what the zoologist usually means by this. 

 The facts — as shown, for instance, in a 

 young fern-plant — are most interesting, but 

 can perhaps be better looked at in another 

 way. Development is accompanied by an 

 increase in size of the successively formed 

 leaves and portions of stem, and the process 

 is often cumulative, going on more and 

 more rapidly as the means increase until 

 the adult proportions are attained. The 

 same specific system of relations may thus 

 find different expression in the developing 

 plant as constructive materials accumulate. 

 I do not want to imply that the question is 

 merely a quantitative one ; quality of mate- 

 rial may be involved, or the explanation 

 may lie still deeper. The point is that the 

 progression is not a necessary one due to 

 some recapitulative memory. 



There are some other classes of facts, 

 clearly cognate to normal individual devel- 

 opment, that seem to require the causal ex- 

 planation. I may mention three : (1) Vege- 

 tatively produced plants (from bulbils, 

 gemma, etc.) tend in their development to 

 pass through stages in elaboration similar 

 to young plants developing from a spore or 

 zygote. The similarities are more striking 

 the smaller the portion of material from 

 which a start is made. (2) Branches may 

 repeat the stages in ontogeny more or less 

 completely also in relation to differences in 

 the nutritive conditions. (3) In the course 

 of continued development there may be a 

 return to the simpler form and structure 

 passed through on the way to the more com- 

 plex. These cases of parallels to, or rever- 



sals of, the normal ontogenetic sequence sug- 

 gest explanation on causal lines, but are 

 difficulties in the way of phyletie recapitu- 

 lation; the first two cases can be included 

 under this, while the third seems definitely 

 antagonistic. On the whole, it may be said 

 that recapitulation can not be accepted for 

 plants without further evidence, and that 

 preliminary inquiry disposes us to seek a 

 deeper and more fruitful method of ex- 

 plaining the facts of development. 



The development of most plant-individ- 

 uals starts from a single cell, and when we 

 compare mature forms of various grades of 

 complexity the unicellular condition is also 

 our usual starting-point. What is not so 

 generally recognized or emphasized is the 

 importance of the filament as the primitive 

 construction-form of most plants. I do not 

 use the word primitive in a phyletie sense, 

 nor in the sense of an ideal form, but to 

 indicate a real stage in independent pro- 

 gressions underlying many homologies of 

 organization. I can not develop this fully 

 here, but wide comparison of independent 

 lines of advance suggests that the main 

 types of progress in complexity of the 

 plant-body have involved the elaboration of 

 the single filament with apical growth and 

 with subordinated "branches." It is gen- 

 erally recognized that various groups of 

 algffi show how a solid multicellular axis 

 may come about, not only by the further 

 partition of the segments of the apical cell, 

 but by the congenital cortication of a cen- 

 tral filament or the congenital condensa- 

 tion of the subordinated "branches" on to 

 the central axis. The algse further show 

 the change from the dome-shaped apical cell 

 of a filament to the sunken initial cell with 

 two, three or four sides. The central fila- 

 ment then only appears, if at all, as a sub- 

 sequent differentiation in the tissue, and the 

 segments serially cut off from the apical cell 

 may or may not bear projecting hair-shoots 



