74 Transactions. 



bases, in the majority of young plants of this age that were examined, 

 show as a tuberous region separated from the first-formed protocorm proper 

 by a more or less marked constriction. In L. cernuum the protophylls are 

 all normally developed on the upper side of the small tuberous protocorm, 

 and not as a lateral extension of it. The writer has, however, out of a 

 large number of young plants of L. cernuum that he has examined, observed 

 that the protocorm in one or two instances showed a distinct tendency to 

 grow laterally, one young plant showing seven protophylls on such an 

 extended protocorm. In older plants of L. laterale it was observed that the 

 original protocorm could often be still distinguished from the later-formed 

 protocormous extension, and that the former easily broke away from the 

 latter in the process of cleaning. 



The further growth of the young plant takes place by the continued 

 lateral development of protophylls, and the consequent extension of the 

 protocorm by their swollen bases, the protocorm increasing in thickness 

 the farther from the original end. The protophylls are more or less 

 arranged in two rows on its dorsal surface, this arrangement indicating 

 that their development, as also that of the rhizome itself, has taken place 

 very regularly. The protocormous rhizome thus formed bears ventrally 

 a mat of rhizoids. It gradually loses its green colour and semitranslucent 

 appearance, and in the fully developed stage has become yellowish and 

 opaque and firm, whilst after the differentiation of the stem-axis both the 

 protophvlls and the rhizoids decay away. The rhizome consists of paren- 

 chymatous tissue throughout, the cells of the central region being smaller 

 and more compact, whilst those nearer the surface are larger, and show 

 air-spaces. A strand of vascular tissue is present in each protophyll, and 

 passes down into the body of the rhizome, where it ends blindly. At the 

 stage at which a stem-apex is differentiated there are from eight to twelve 

 protophylls, and the rhizome is from 3 mm. to 5 mm. in length and from 

 1 mm. to 2 mm. in thickness. In one instance it was observed that the 

 rhizome had forked into two equal branches, and that on each of these a 

 stem was developing. 



The stem-axis arises at some point on the dorsal surface of the rhizome 

 towards its growing end, or even almost at the end itself, and is indicated 

 by the aggregation of protophylls. At the same time, vascular tissues 

 are initiated from the stem-apex and extend down into the body of the 

 rhizome, receiving on the way strands from the neighbouring protophylls. 

 In the rhizome these vascular tissues bend round at a sharp angle, and, 

 surrounded by a slight zone of sclerenchyma, take a course through the 

 body of the rhizome, though nearer its dorsal surface, towards its growing- 

 end. The latter at the same time grows outwards and downwards to form 

 a finger-like protuberance into which the vascular tissues pass. Thus the 

 extension in length of the protocormous rhizome is brought to a close by 

 the initiation of this exogenously developed first root. The writer has 

 observed that in the young plant of L. cernuum the vascular tissues of the 

 stem behave in the same way as in L. laterale. They lead down bodily into 

 the upper region of the protocorm, and thence decline towards the finger- 

 like protuberance of the rhizome, which is the first root, though in this 

 species the angle of declination is more gradual than in L. laterale. The 

 course of the main vascular strand in its relation to the protocorm just 

 described may be compared with what obtains in the young plant of 

 L. clavatum and other species, where the vascular system does not extend 

 into the tissues of the large intraprothallial foot. All subsequently formed 

 roots in the young plants of both L. laterale and L. cernuum emerge 



