188 Transactions. 



as the long-drawn-out forms there are short, comparatively massive indivi- 

 duals. These correspond to such a group of lobes with its associated fungal 

 region as has just been described, the development of the massive body of 

 tissue having proceeded to an unusual extent. Sometimes it is seen that 

 in these massive prothalli there has been an original first-formed, long- 

 drawn-out portion which has withered away, but always the subsequent 

 growth of the prothallus is confined to increasing the massiveness of the 

 main tissues and does not result in any further extension in length. In 

 many cases, especially at the actual crown of the prothallus, the group of 

 lobes has withered, there being a consequent browning of the upper surface 

 at this point. In some instances, instead of lobes being present, there are 

 only feebly developed warty excrescences. Again, in other instances the 

 lobes are fairly thick in form. Serial sections of the prothalli show that 

 the fungus swellings are all identical in nature and correspond \ery closely 

 with what is found in the prothallus of L. laterale. The peripheral cells 

 contain the spherical masses of hyphae, while those in the interior of the 

 swelling show the fungus only within the cell-walls. These latter cells have 

 not assumed such a definite tissue-form in accordance with their particular 

 function as is sometimes to be seen in L. cernuuni. The initial stase in the 

 formation of a fungus area is sometimes to be seen, one or two epidermal 

 cells showing the presence of the fimgus, but no swelling having yet taken 

 place. In not a few prothalli, both of the massive and of the long-drawn- 

 out form, the actual first-formed region nearest the original spore was to 

 be seen. Moreover, several very young prothalli were found. There is 

 first a longer or shorter filamentous stage, in which the young prothallus 

 is only one cell wide, after which it proceeds gradually to increase in width 

 as it lengthens. The prothallus is from the first quite green in colour, and 

 infection by the fungus seems to take place subsequently to these early 

 stages of growth. However, in one or two prothalli of the massive form I 

 noticed that the original but very short filament passed immediately into 

 the bulky fungus-containing tissue, the complete prothallus having very 

 much the form of an inverted cone with the spore filament at its apex. 

 The resemblance of this to the clavatum type of prothallus is obvious. 



The prothalli of the three New Zealand species which belong to the 

 section Cernua are thus seen to be in a condition of great plasticity. The 

 main reasons for the modifications of the typical cernuum form seem to be 

 the varying depth at which the spores germinate, together with the extent 

 of infection by the fungus element, this resulting in all three species, and 

 especially in L. ramulosum, in a form of prothallus more or less elongated, 

 which develops rhizoids at intervals along its length, a form which may be 

 well compared with that acquired by the humus-growing, wholly sapro- 

 phytic prothalli characteristic of the Phlegmaria type. The various forms of 

 the prothalli of L. Selago and L. ramulosum show how it is possible for both 

 the much-branched Phlegmaria type and the compact, more massive clavatum 

 or complanatum type to arise as modifications of the original form. The 

 prothalli even of L. cernuum and L. laterale give indications of this. This, 

 taken in conjunction with the fact of t\\e great plasticity of the species as 

 seen in all their main characters, and the occurrence of numerous transi- 

 tional forms both between one species and another and also between one 

 type and another, indicates that the main natural divisions of the genus 

 correspond with its biological distribution, and that the different sections 

 into which the species are classified by systematists bear a certain definite 

 relationship to one another. Only a comparative examination of the chief 



