OF ARTS AND SCIENCES. 55 



E. P. Wright, Curator of the Harveyan Herbarium at Trinity Col- 

 lege, Dublin. With this specimen, our plant was carefully and 

 critically compared, and was found to agree with it in every point 

 of structure and habit. There can be no reasonable doubt that the 

 specimens received from Messrs. Ilolden and Harger belong to the 

 Tuomeya Jluviatilis of the Nereis. 



The systematic position of Tuomeya is a matter of considerable 

 interest and importance. Harvey says, on page 62 of the Nereis : 

 "The plants referred to this order [Batrachospermece) naturally 

 group themselves into two suborders, distinguished from each other 

 by the habit of the frond, but closely related in structure and fructifi- 

 cation, and as it seems to me inseparably connected by the genus 

 Tuomeya, which unites in itself the characters of the seemingly so 

 dissimilar genera Batrachospermum and Lemanea" An exact knowl- 

 edge of the relation which Tuomeya bears to Lemanea and Batracho- 

 spermum respectively, requires a careful comparison of the details 

 of the structure and development to be found in these three genera. 

 As Harvey had only a few dried specimens of Tuomeya at his dis- 

 posal, he did not undertake to do this. Indeed, he remarks that he had 

 not even ventured to make a drawing from them. Dried specimens, 

 as far as my experience goes, are peculiarly unsuitable for study, as 

 the various cells do not recover their original size and shape at all 

 well. The manipulation of plants which have been long dried is a 

 ditficult and unprofitable task. Specimens which have been preserved 

 in weak alcohol (of a strength of about fifty per cent) are much 

 better for the purpose, but the hardening of the elements produced 

 by the alcohol imparts a rigidity and a brittleness which are detrimen- 

 tal to obtaining the best results. Fresh material is readily prepared 

 for the microscope, and shows the details both of structure and de- 

 velopment most satisfactorily. The work whose results are summa- 

 rized below has been done entirely upon the living specimens, and the 

 author has thus been able to obtain a more complete knowledge of the 

 life history of Tuomeya than would have been possible under any 

 other circumstances. Through the kindness of Mr. Holden, he has 

 been supplied at frequent intervals with fresh specimens, not only of 

 Tuomeya, but of various species of Lemanea and JJatrachospermum as 

 well. With such facilities, it has been possible to compare the struc- 

 ture and development in these genera, point for point, and to deter- 

 mine with a certain degree of definiteness the exact relation existing 

 between them. 



The method of investigation has been a comparatively simple one. 



