482 DB. MAXWELL T. HASTEBS OK 



Larches indicate an arrest in growth of the axis ; but it is very 

 common to find a shoot elongating, and bearing the leaves in 

 scattered spirals. Sometimes these spirally arranged and scat- 

 tered leaves in Pinus are merely the bud-scales or " perulae " which 

 have assumed a leafy development. Such leaves also have essen- 

 tially the same anatomical structure as the ordinary ones. So, 

 in the case of the Eetinosporas, in the "larval" state the 

 leaves are free and detached from the stem, but in the mature 

 plant the leaves remain in adhesion with, or never separate from, 

 the stem, except at the tips. The internal structure of the 

 various forms of the leaves in Betinospora and Juniperus is 

 essentially the same, but more spongy in the faster-growing 

 leaves. In Libocedrus decurrens it seems as if the axillary bud 

 were also adherent to the stem, and uplifted with it during its 

 growth ; for it proceeds from the stem, not at the organic base 

 of the leaf, but at the point where the leaf becomes detached 

 from the stem. This may be the result of an arrest of growth. 

 But if this be so, it is by no means easy to determine what 

 causes the arrest, what stimulates the progress, particularly 

 when these are confined to one or a few branches. Similarity 

 of surroundings and outward conditions naturally engenders a 

 similar disposition of parts: thus in the leading shoot of a 

 Bicea the leaves are in scattered spirals, while on the hori- 

 zontal branches the spiral is so masked by the crowding of the 

 leaves and the twisting that occurs at their base that there is a 

 pseudo-distichous arrangement, and the uppermost leaves are 

 often shorter than the lower ones. In the leading shoot, in such 

 cases, we have an analogous arrangement to what occurs in 

 Lycopodium ; on the lateral branches the arrangement suggests 

 that of Selaginella. The interest attaching to these varied forms 

 of one and the same individual is enhanced by their suggestiveness 

 in regard to the possible lineage of the species, a matter hardly 

 more than broached. They may possibly represent the condition 

 of some progenitor ; or such a genus as Betinospora (so called) 

 may be one in course of formation. The student of fossil plants 

 might help us to the solution of this problem. 



In the following table the single line — indicates the occur- 

 rence of a species, the double line = that of a genus, in the dis- 

 trict to which the column refers. The distribution of the fossil 

 genera is not indicated in detail. 



