PIN US S YL VESTRIS. 1 6 7 



between the cells forming the several rows of palisade 

 tissue." 28 



The four bundles of each pair of leaves have the 

 normal orientation, the xylem portions all facing a 

 common center and the phloem the periphery. The 

 imbedding of the bundles in a mass of colorless tissue 

 surrounded by a sheath is common among the pines 

 and their allies. 



In this central tissue many of the cells are tracheides 

 (see fig. 7), as pointed out in the laboratory part ; they 

 are arranged in a special manner and are characteristic 

 of ConiffTG* These tracheides during the activity 

 of the leaf contain water, 80 and hence have been, called 

 transfusion tissue by H. v. Mohl 31 and others. 



The existence of occasional poorly developed resin 

 passages in the xylem of the leaf bundles is to be noted, 

 as it has been denied by Corry 33 and Van Tieghem. 33 

 (See fig. 7 r). 



In comparing the reproduction of the pine with 

 that of the fern and earlier forms we find advances of 

 much interest. In the fern, as in the moss and liver- 

 wort, the spore grows into a structure, which bears 

 the reproductive organs. In the moss and liver- 

 wort this sexual or thalloid stage comprises by far the 

 larger part of the life cycle, while the asexual stage 

 (the so-called fruit) is small and quite unable to lead 

 an independent existence. In the fern the thalloid 



88 Op. cit., p. 355. 



* 9 Cf. DeBary, Comp. Anat., p. 378 et seq. 



30 Strasburger, op. cit., p 234. 



31 Bot. Zeitung, 1871, No. i, 2. 



32 Op. cit., p. 359. 



33 Ann. Sci. Nat., Ser. V, xvi (1872), p. 189. 



