HoLLOWAY. — Studies in the New Zealand Species of Lycopodium. 231 



functioned in the extension in length of the prothallus and in the production 

 of sexual organs and processes, the growth in length of the prothallus being 

 renewed after the formation of each generative area. If an archegonium 

 had been fertilized and an embryo formed, all the food-supply of the 

 prothallus would have been concentrated around the growing embryo, and 

 hence the prothallus would have ceased to elongate. In the prothaUus 

 shown in fig. 51 there has probably been no intermission in the functioning 

 of the apical meristem, with the result that this prothallus approximates 

 more to the cylindrical form of the epiphytic type. In the prothalli shown 

 in .figs. 52-54 there has been an exceptionally extensive development of 

 generative tissue, giving to these prothalli the curious step-like form. 

 From these elongated prothalli and from the irregularly-grown, more 

 massive forms shown in figs. 58 and 59 it would appear that the repeated 

 fresh infection of the prothallus by the fungus has enabled it to grow on 

 far beyond its original cermmm-lik.e form. In such a prothallus as that 

 shown in fig. 51 the position and appearance of the meristem are similar 

 to the ordinary cernuum type, although it has been able to function for a 

 much longer period than in L. cernuum. In the other elongated prothalli 

 shown in figs. 50 and 52-54 the position and form of the meristem is 

 somewhat modified on account of the repeated development of the genera- 

 tive tissue, so that the actual growing apex is small and somewhat displaced. 

 There is never a definite group of apical meristematic cells present, the 

 whole of the growing head functioning in this respect as in L. cernuum. 

 The very compact cone-like prothallus given in fig. 56 also shows the same 

 type of meristem, there being no tendency to a localized, marginal, ring- 

 like meristem as there is in the compact surface-growing forms of L. Selago. 

 Thus, although the prothalkis of L. ramulosum in its two forms may be com- 

 pared on the one hand with the compact cone-like forms of L. Selago (and 

 so also of L. clavatum and L. complanatum), and on the other hand with 

 the elongated cylindrical form of L. Phlegmaria, &c., this comparison is 

 by no means a close one, for the position of the meristem shows that 

 L. ramulosum belongs always to the cernuum type. It is significant to 

 note that these main types of Lycopodium prothalli are in a plastic con- 

 dition, and the variations which they show make it quite permissible to 

 conjecture how the different methods of growth could have originated. 



The mature prothallus of L. laterale also conforms to the cernuum type 

 in the position of its meristem, although here too the normal form of the 

 main prothallial body is sometimes considerably modified by its continued 

 growth. 



Relation ' of the Young Plant to the Prothallus. 



Since the prothallus of these species is always situated at the surface 

 of the ground, the young plant possesses chlorophyll from a very early 

 stage. As soon as it emerges from the tissues of the prothallus it proceeds 

 to form the characteristic tubercle which Treub called the " protocorm," 

 on which abundant rhizoids are produ^ced. At the same time the first 

 " protophyll " arises on the tubercle, showing numerous stomata. Thus 

 the developing plantlet early becomes independent of the prothallus in 

 the matter of food-supply. A protocorm is formed in the young plant 

 of all three New Zealand species which belong to the Cernua section. 

 Young plants attached to their parent prothalli are shown in fig. 72 

 {L. cernuum), in figs. 46 and 48 {L. laterale), and in figs. 51, 56, 58, 60, 

 and Plate XV {L. ramulosum). Other figures are also given in Part I of 

 this series of papers. 



