HoTiLOWAY. — Studies in the New Zealand Species of Lycopodium. 189 



characters of both gametophyte and sporophyte generation can show which 

 particular characters are more fixed than others, and so indicate what is 

 the nature of this interrelationship between the sections of the genus. 



The Young Plant. 



In all the species belonging to the two sections Inundata and Cernua 

 whose embryogeny is known the embryo plant passes through a protocorni 

 stage. Goebel has described this in L. inundatum, and Treub in L. cermmm. 

 In two previous papers (15, 16) I have described the protocorm of 

 L. laterals, and in the second of these papers I have given a fairly complete 

 account of it not only in this species, but also in L. cernuum and L. ramidosum. 

 Chamberlain (7) has also published an accoimt of the protocorm of L. laterale. 

 In Part II of these Studies (17) I have demonstrated the presence of a 

 protocorm in adventitiously developed plants of L. cernuum and L. ramu- 

 losum, and have shown that the large protocormous rhizomes of the latter 

 species can branch, give rise to two or even three stems, bud off bulbils, 

 or by partial decay break up into a number of distinct portions, each of 

 which can develop into a young plant. Goebel also has described adventi- 

 tious protocorms in L. inundatmn. There will be no need for me to repeat 

 here the description of this organ as it occurs in the three New Zealand 

 species, beyond pointing out the facts relating to its variability in form. 



In the case of L. cernuum I have shown (16, pp. 283-84) that usually 

 the growth in size of the protocorm ceases after the first three or four 

 protophylls have been formed, but that in some instances a certain amount 

 of lateral growth takes place, as many as seven protophylls being formed 

 along the top of the extended protocorm before a stem-axis is initiated. 

 Since that account was written I have examined another colony of young 

 plants of L. cernuum, several of which showed very large protocorms quite 

 comparable in size to the largest of those of L. laterale found by me. It is 

 thus apparent that whereas under normal conditions this peculiar structure 

 does not assume a large size in L. cernuum, yet under certain conditions, 

 occasioned probably by a dry season, it may function for a much longer 

 period and assume a much larger size. 



In both L. laterale and L. ramtdosum the protocorm is also very variable 

 in size, although it is much larger than it usually is in L. cernuum. In the 

 paper quoted above (16. pp. 277-83) I have set myself to show that the 

 large size of this organ in L. laterale, and also in L. ramidosum, is merely 

 a special adaptation suited to carry the young plant over the dry season. 

 In all these New Zealand species which possess the delicate short-lived type 

 of prothallus the young plants are formed during the spring and early 

 summer. During the dry months of midsummer probably the majority 

 of them die, except those in exceptionally favourable situations, or those 

 whose protocormous rhizome has become sufficiently tuberous to be able 

 to withstand a period of drought. Then, as the wet season comes round 

 again, growth is resumed and a stem-axis is initiated. 



According to this view the protocorm is a plastic organ whose form 

 and importance is mainly dependent upon external conditions. This also 

 suggests that the protocorm in general, as it occurs throughout the sections 

 Inundata and Cernua, is a physiological specialization. This is the view 

 taken by Bower (3, pp. 225, 355). Goebel also (14) was not able to see 

 any phylogenetic significance in this organ. 



Thus there are certain consistently present characters in these two sections 

 which indicate that they together form a natural division of the genus 



