Febkuaky 23, 19 



SCIENCE. 



293 



of the mode of origin of the secondary 

 roots from such a root, we find that they 

 are formed in all their parts, entirely 

 -within the central cylinder or plerome 

 strand of the mother root. We have thus 

 the cortex and piliferous layers of the 

 daughter root, which are properly the 

 derivatives of the apical meristems known 

 as the periblem and the dermatogen, and 

 not of the plerome, originating in this case 

 from the plerome or its equivalent. A 

 logical fallacy thus arises, if we regard the 

 morphological value of the tissue-systems 

 of the root as determined from the meri- 

 stems from which they take their origin. 

 Further, if we take the case of the stem 

 of the Pteridophyta, where alone among 

 stem organs, the so-called apical meristems 

 can in general be somewhat clearly distin- 

 guished, we reach equally illogical con- 

 elusions. Let us, for example, follow cer- 

 tain recent writers in regarding the whole 

 complicated fibrovascular system of the 

 rootstock of the common bracken fern, 

 Pteris aquilina, together with its interposed 

 ground tissue, as constituting a single 

 hypothetical circular stele or central cyl- 

 inder, because all these tissues are derived 

 from the plerome strand of the growing 

 end of the rhizome. If in all cases the 

 plerome were as generously large as it is 

 in Pteris aquilina and sufficiently broad 

 to include the fibrovascular strands, to- 

 gether with their interposed fundamental 

 tissue, we might successfully sustain the 

 thesis that there is but one central cylinder 

 and the plerome is its prophet. Unfortu- 

 nately, however, in some cases the plerome 

 proves to be a misfit and is smaller than 

 the central cylinder, which it should en- 

 tirely include. As a result in some of the 

 true ferns, essential tissues of the fibro- 

 vascular bundles, such as the pericycle, the 

 phloem and even part of the tracheary 

 tissues are left in oiiter morphological 

 darkness, because they do not originate 



from the plerome, but from the periblem. 

 In a recently published woi'k. Professor 

 Campbell even states that in the mature 

 stem of Equisetum only the pith is 

 formed from the plerome, all of the fibro- 

 vascular tissues being left outside. He 

 concludes that in Equisetum the fibro- 

 vascular bundles do not form a part of the 

 central cylinder. This is surely Hamlet 

 with Hamlet left out, and may perhaps 

 stand as the reductio ad absurdum of 

 growing-point morphology. If our not 

 vei'y remote posterity compare our specula- 

 tions in regard to the morphological value 

 of the growing point in plants, with those 

 well-known discussions of medieval doctors 

 as to the number of angels who might suc- 

 cessfully stand on the point of a needle, 

 our neglect of logic will probably not ap- 

 pear less absurd than their entire disregard 

 of facts. 



The two examples just discussed suffi- 

 ciently illustrate the present condition of 

 transition in morphology. Although the 

 ancient doctrine of preformation has long 

 been consigned to the limbo of oblivion, it 

 has nevertheless a disguised survival in the 

 hypothesis that the organs of tissue-sys- 

 tems of the higher plants can definitely be 

 traced back to an origin from certain 

 definite primordia. This hypothesis ap- 

 pears destined to become as obsolete in 

 morphology as that of predestination is 

 in theology. We have in fact arrived at 

 that stage in morphological enlightenment 

 where, with the complete abandonment of 

 all obscurantism, we call a spade a spade, 

 meaning by a spade that which performs 

 or has performed the functions of a spade. 

 Nothing appears clearer in the present 

 stage of our knowledge than that with Pro- 

 fessor Goebel we must regard the organ as 

 the tool or apparatus of a function and the 

 organism as a complex of apparatus com- 

 bining a number of functions. Yet even 

 if it be true that the organ is but the tool 



