THE STELAR THEORY; A HISTORY AND A 



CRITICISM. 



PART I. 



IN the study of the histological anatomy of plants, apart 

 from the structure of the individual cell, the greatest 

 advances of the last two decades have been made rather by 

 the establishment of new points of view than by the dis- 

 covery of new facts. Twenty years ago the solid founda- 

 tions of the subject had been securely laid, and a consider- 

 able portion of the imposing fabric of histological detail 

 which now rests upon them had already been built up. 

 This fact is most clearly brought out by the masterly 

 summary of existing anatomical knowledge published by 

 De Bary in 1877. But splendid monument as it is of its 

 author's unsurpassed knowledge of his subject, there can be 

 few who have not felt that the Vergleichende Anatomie 

 is, as a whole, essentially unreadable. Compare it, in 

 imagination, with Sachs' Vorlesungen or with Haber- 

 landt's Physiologische Pflaiizenanatomie , and we are 

 forced to recognise that De Bary's work is rather an ency- 

 clopaedia than a piece of great scientific literature. The 

 cause is to be found in the simple fact that there did 

 not exist in 1877 a philosophy of the morphological aspect of 

 the subject capable of informing " an epitome of the pre- 

 sent knowledge of 'the Anatomy of the Vegetative Organs 

 of Vascular Plants,' " as the idea of adaptation informed the 

 works of Sachs and Haberlandt. 



It is nothing less than the establishment of such a 

 philosophy that we now owe to the great Frenchman, Van 

 Tieghem. The most important part of his ideas is con- 

 tained in what we may call the Stelar Doctrine of Vascular 

 Tissue, and it is with this that we shall here be exclusively 

 concerned. 



Although the foundations of the stelar theory were laid 

 many years ago, outside France it has made its way very 

 slowly. In Germany even now it is apparently ignored 



