CHAPTER II 



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HYPOPLASIA 



21 



We speak of Hypoplasia if an organism or one of its 

 parts does not attain a normal development but ends its de- 

 velopment prematurely, so that forms or characteristics ap- 

 pear fixed as final, which, under normal conditions, "belong 

 only transitorily to the organisms or organs concerned. To 

 put it briefly, Hjrpoplasia is defective development, and its 

 products remain in one or in several respects belov; the re- 

 sults of normal development. The development of the organ- 

 isms or organs appears as though "arrested", on v;hich account 

 we can term the products of a hypoplastic process arrested 

 develQ-pments. • From the aforesaid it follows that in 

 treating of arrested developments, v/e will be concerned only 

 with forms and pecularities of the organisms and thier parts, 

 already known from the ontogeny pf normal individuals. 



The discussion of arrested-development devolves upon 

 either morphologists or anatomists, according to whether the 

 arrestment may be recognized in the maturing of whole organs, 

 or in the development of the cells and tissues. On the morph- 

 ological side a large number of observations have been col- 

 lected and utilized scientifically. They prove that the 

 arrested development of similar organs can result very dif- 

 ferently, since very different stages of the normal progress 

 of development appear to be "fixed". In addition to this, 

 it is proved that those processes of growth and differenti- 

 ation are not always equally arrested, which in a normal 

 course of development, are associated in time and place. 

 Thus, for example, very different kinds of arrested-devel- 

 opments may be pointed out in leaves . In many such cases , 

 12 the leaves vary from those normally developed in the small- 

 ness of their size. The etiolated sprouts of many plants 

 furnish examples of this. In other cases the leaves are 

 less retarded in size than in form; for example, in the case 

 of specimens of Sagittaria grown under water, of the Ret- 

 inospora form of many conifers, different galls on the tips 

 of the shoots, etc. Thirdly, the form of the leaf may re- 

 main undeveloped. Either the initial folding and curling 

 of the leaf blade is retained, as in the artificially forced 

 branches of Aesculus, Gingko, etc.; in the etiolated speci- 

 mens of Viola; in many leaf galls (Phytoptus mites on Rosa, 

 Fagus, etc.); or the inclination of the leaf to the axis re- 

 mains as it was at first,- for instance, in willow leaves 

 unfolded under water, in the galls on the tips of Glechom 

 shoots fCecidomyia) , etc. Of course the leaves may also 

 "remain below the normal" in more than one respect. The 

 examples here chosen should demonstrate at the same time that 

 arrested developments of the same character can be produced 

 by the most varied influences, 



1« The word Hypolasia is derived from the terminology of 

 the medical science; the term arrested development has long 

 been familiar to botanists. 



2, Compare especially Gobsl, Organographie , 1898, p. 121, 

 and the literature quoted therein. 



