320 Scientific Proceedings, Royal Dublin Society. 



necessary for the attachment of the two ovules, whose volume is much 

 greater than that of the scale. 



The same gradual transition is characteristic of Pseudotsuga. 



B. The Ovule. — Attention has already been directed (5) to the micropylar 

 arrangement in Larix, an arrangement which it shares with the hitherto 

 unique ovule of Pseudotsuga, as described by Lawson (15). So similar are 

 the two ovules that the likeness can best be emphasized by quoting Lawson's 

 account of the ovule of Pseudotsuga Douglasii with reference to PI. XVIII, 

 fig. 7, which represents a median section of the ovule of Larix leptolepis. 

 Lawson says : — " The pollen-receiving device in Pseudotsuga is quite peculiar, 

 and unlike anything yet described for Gymnosperms. Tor some little time 

 after pollination the nucellus presents the form of a small protuberance, 

 with a perfectly rounded apex. The integument extends for a considerable 

 distance beyond the nucellus. At a point immediately above the apex of 

 the nucellus the integument bends inward in such a fashion as to partly close 

 or narrow the micropylar canal, and then sharply bends out again. This 

 results in the formation of a distinct structure midway between the apex 

 of the nucellus and the mouth of the micropyle. As a result of this peculiar 

 curvature of the integument, the micropylar canal is not a straight passage 

 of uniform width, but consists of two chambers, one immediately above the 

 apex of the nucellus, and the other near the mouth of the micropyle. In 

 addition to this narrowing in the middle region of the micropyle the integu- 

 ment is still further modified. The extremity of the integument, which 

 forms the mouth of the micropyle, is folded inward. On the inner surface 

 of this infolding extremity numerous fine hair-like processes are present. 

 A close examination makes it clear that they were not cellular in structure, 

 but were merely outgrowths from the external walls of the epidermal cells. 

 They serve very effectively, however, as a stigmatic surface." The hairs in 

 the Larix are firmer, and are large and small, the latter so compact as to 

 give the impression of a basal cellulose plate (the dark, thickened mass in 

 the figure). " The pollen grains were invariably in the upper chamber of 

 the micropyle, and frequently entangled in the hair-like processes of the 

 mouth." 



So far the two genera are much alike, but there is one remarkable 

 difference. The pollen-receiving device in Larix apparently always acts just 

 as in Pseudotsuga, no grains ever having been seen on the nucellus at this 

 stage. In passing, it should be stated that pollination is usually completed 

 by mid-March, when the opening of the micropyle gradually closes over. 

 To return to the difference between the genera, we recall the unique fact 

 that in Pseudotsuga the grains are described by Lawson as germinating in 



