566 SUMMARY OF CURKENT RESEARCHES RELATING TO 



of the nucleolus. During anaphase, this substance divides into two groups 

 of rods which pass to the poles, and to each rod two of the true chromo- 

 somes become attached. The nucleus is reconstituted at the^expense of 

 the rods and chromosomes ; vacuolisation occurs, and a nucleolus is 

 formed by condensation, and during this process the rods and chromo- 

 somes lose their separate identity. The nuclear membrane is nothing 

 but a peripheral layer of protoplasm. The nuclear network is gradually 

 re-formed during telophase. The spindle of Sjnrogyra is purely cyto- 

 plasmic, the fibres being formed outside the nucleus and penetrating 

 into its interior. 



Structure^and Development. 

 Veg-etative. 



Tracheids of Wood of Conifers.* — W. Krieg has studied the 

 stratification of the tracheid-membranes in the Coniferge, and finds that 

 it chiefly occurs in the " red " wood of the horizontal branches, and is 

 confined within the annual ring to the autumn wood. It depends upon 

 an internal differentiation of the membrane into alternate thicker and 

 more delicate layers, and the markings always run obliquely to the left. 

 The fissure-formation is not identical with the striping, but is dependent 

 upon it. The spiral thickening is not an internal differentiation, but a 

 local thickening of the innermost membrane-layer in the form of spirals, 

 rings, etc. All markings, spiral thickenings, and pit-formations are the 

 product of living plasmas, but their physiological significance is at 

 present unknown. 



Comparative Anatomy of the Polemoniaceae.f — G. Hiiller gives an 

 account of his investigations of the leaf, pollen, and testa of the 

 Polemoniacese. As regards the leaf, several of the species, including the 

 genera Cantua and Gohcea, have stomata only on the under side, but both 

 sides are usually thus provided ; in Phlox Hordii alone are they more 

 numerous on the upper side. There are no subsidiary cells. As regards 

 the mesophyll, the bifacial arrangement occurs in Bonplandia, Cantua, 

 Cohcea, and species of Gilia, Phlox, etc., the centric in other species of 

 Gilia and PMox, and in two species each of Collomia and Loeselia. In 

 Phlox longifolia and certain species of Gilia the mesophyll has water- 

 storage tissue in which the nerves are imbedded. 



The midrib in some cases (species of Gilia, Collomia, Loeselia, and 

 Phlox) has single bundles of sclerenchyma, or small groups of such, lying 

 either in the xylem or the phloem, or above or below them ; in others 

 there is a semi-lunar mass of sclerenchyma below, and a complex of 

 sclerenchyma bundles in contact with the leptome or above the xylem. 

 Two anomalous types of midrib structure are met with ; in a few cases 

 (species of Gilia and Phlox Douglasii) a large mass of sclerenchyma 

 separates the leptome into two islands, and this is carried further still in 

 other species of Gilia, the xylem and phloem being divided into several 



* Beih. Bot. Centralbl., xxi. (1907) pp. 245-62 (4 pis.). 

 t Tom. cit., pp. 173-244 (1 pi.). 



