3Q4 



THE GENUS DACRYDIUM. 



So/and. in Forst. PI. Escul. 80. 



I. HISTORICAL. 



Solander in G. Forster, "Plant. Esculent.," established this name in 1786. 

 The genus does not occur on the mainland, being restricted to Tasmania so far as 

 Australia is concerned. 



It has, however, a wide geographical range, being found in New Zealand, 

 New Caledonia, the Mala}' Archipelago and Peninsula, Borneo, and Chili. Ettings- 

 hausen (I.e., p. loi, pi. VHI) describes and iigures one fossil species of Dacrydiiim 

 from Emma\ille, New South Wales. 



II. SYSTEMATIC. 



The Dacrydiums are average forest trees, having linear, flat, and 

 spreading dimorphic leaves in the young stage, and in the mature state small 

 and closely imbricated ones. 



The flowers are dicjecious. Male amentum terminal, ovoid or cylindrical. 

 The microsporophylls spirally arranged, imbricate, sessile, shortly contracted at 

 the base, with an introrse spur-like connective ; microsporangia 6 to 20, in two 

 rows opening laterally. Microspore oval or oblong. 



The development of the pollen in the gymnospermous genus Dacrydium 

 is interesting, because, according to the account conti'ibuted by Miss M. S. Young 

 to the Botanical Gazette, September, 1907, a number of cells are formed in what is 

 technically known as the microgametophytc. The spore passes out of the single- 

 cell stage when a small prothallial cell is cut off ; by another division of the vegeta- 

 tive nucleus a second prothallial cell is formed, and in a similar way a third, the 

 generative cell, is produced. The generative cell gives rise to a sterile and a so-called 

 body cell, the progenitor of the sperm cells. As the second prothallial cell not 

 infrequently divides, the mature pollen grain may show as many as seven nuclei. 



Female amentum tcnninal, solitary, consisting of a few small, thick macro- 

 sporophylls in a short spike, or one individual sporophyll, witli a macrosporangiuni 

 at first anatropous and finalh' orthotropous. 



Fruit cones small, erect, surroiiiidcd a1 tlie base by a cup or disk, ovoid 

 oblong, the outer integument memljranous, llir inner tliickcncd and liaid. 



