420 Transactions. 



a form as 0. vulgatum, which approximates more to the usual pteridophytic 

 type of embryo. 



The presence of the "protocorm " in the embryo plant of certain species 

 of Lycopodium has given rise to another suggestion with regard to the 

 origin of the free-living sporophyte — namely, that the protocorm was the 

 precursor of the leafy shoot. Against this it has been urged, especially 

 by Bower (1), that the embryo of Lycopodium is prone to parenchymatous 

 swellings, and that the protocorm is best regarded as a physiological 

 specialization. My own study of the large development of this organ in 

 the two New Zealand species L. laterale and L. ramulosum (4, 5) led me 

 to conclude that its abnormal size in these two species could be put in 

 connection with the fact that the young sporelings were required to tide 

 over a summer season, during which their natural boggy habitat would be 

 usually dried up, before they could establish themselves, and that the manner 

 of development of their protocormous rhizome was capable of a physio- 

 logical explanation. I concluded that this lent weight to the theory that 

 the Lycopodium protocorm in general may best be interpreted in this way 

 (4, p. 289). I was careful, however, to add that the fact that this organ 

 is characteristic of two out of the five sections of the genus L,ycopodium, 

 and is also present in a specialized form in Phylloglossum, indicates 

 " a considerable degree of antiquity for the protocorm within the genus 

 Lycopodium." Vegetatively-produced plantlets of these New Zealand 

 species possess a basal protocorm (5), as Osborn also (13) has shown in 

 plantlets of Phylloglossum produced on detached leaves. This author 

 inclines to regard the tuber of Phylloglossum as of physiological importance 

 only. Since writing my first accounts of the Lycopodium protocorm I 

 have found at the close of a dry summer season a colony of young 

 sporelings of L. cemuum growing upon a roadside clay cutting in 

 which this organ was as largely developed through the formation of a 

 rhizomatous extension as in the other two New Zealand species men- 

 tioned (6, p. 189). This is unusual, for in L. cemuum the stem- 

 axis is generally initiated early on the protocorm, and it indicates 

 that the unusual conditions were the cause of this extra development. 

 Recently Kidston and Lang (9) have described under the name Homea 

 Lignieri a rootless protocormous plant from the Early Devonian of 

 Scotland which " retains in the adult condition an organization comparable 

 to the protocorm stage in the species of Lycopodium.. The relation of the 

 aerial stems of Homea to the rhizome is similar to that of the protophylls 

 to the protocorm in Lycopodium " (9, p. 620). It is, of course, a perfectly 

 legitimate criticism to make that even in this archaic plant the protocorm 

 is merely a physiological specialization called forth by precisely the same 

 conditions as govern the life of the modern swamp-growing species of 

 Lycopodium, and the fact that the authors have indicated (9, note, p. 612) 

 that an intercellular fungus is present in the rhizome is of considerable 

 significance in this respect. However, the plant in its general organization 

 is obviously primitive, and is associated with other types of plants of very 

 simple structure, and, belonging as it does to a group which comprises the 

 earliest known land-plants, can be considered as lending great weight to 

 Treub's theory of the protocorm. If the protocorm can be regarded as 

 primitive, it is, of course, open to be interpreted either as an organ by 

 which the supposed sporogonium-like ancestor of the Lycopods first 

 attained independence of the gametophyte, or as a more or less modified 

 representative of a possible thalloid ancestor. 



