1880.] NATURAL SCIENCES OF PHILADELPHIA. 231 



In Eig. Ill the testa has been removed from the cotyledon (c). 

 The two lobes are distinctlj' separate, iio) bearing the oi)erc'ulum 

 under which the upper part of the plumula is concealed. The 

 radula (r) is further developed ; in (g) we have the bud of the 

 second frond. The section in Fig. lY sliows the plumula (p) 

 fully developed into the first frond, which in (r) sends down its 

 radula. The angle formed by this frond and the axis of the cotj'- 

 ledon is about 120°. Corresponding to the first figures (c) and 

 (»'), are the lobes of the cotyledon. (^We have to bear in mind tliat 

 all the figures represent thin sections through the different parts.) 

 In rcalit}' the lobes of the cotyledon are two parallel obovate 

 sheets enclosing the basal part of the much larger, likewise obovate 

 frond. In this figure the gemma has been so far developed as to 

 show in ( f) the fissure in w-hich the bud of the third frond is 

 being clifierentiated. Its elongated inferior part (p') is the 

 secondarv plumula. In using a high power, the microscope will 

 show in the region indicated by (x) several rows of very wide cells. 

 Here the separation of the frond from the cotyledon will take place. 



In Fig. V this separation is complete. In (p') we have the 

 yet more elongated plumula, in (r') the radula of the second frond, 

 and (/') shows again the fissure for the formation of the third 

 individual. 



The section represented in Fig. YI goes through the radula (r), 

 showing a central vascular bundle (i) surrounded bj' a tissue of 

 very loose, almost hj-aline cells {I). In the further development 

 of the rootlet this outer tissue will follow the growth of the vascu 

 lar bundle to a certain extent ; then its basal part will be sepa- 

 rated from the frond. But, remaining in connection with the 

 more and more extending vascular bundle, this wide-celled tissue 

 will form at the top of the full-giown root the well-known hood or 

 calyptra, characterizing the roots in all Lemnacese. 



The last two figures (YII and YIII) need no further explanation. 

 The^' show the formation and completion of the second frond (pO> 

 from which the third individual will be developed in the same 

 way as has been illustrated in the first figures. In i^p") we have 

 the plumula, in (r") the radula of the third fronds ; (/") in 'Fig. 

 YIII shows the fissure for the formation of the fourth individual. 



In this way we see the propagation continued through the 

 summer, plant after plant being formed from a cleft of the pre- 

 ceding individual through a process of prolification. 



