INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 909 



that in tlie lees common but still nnraerous cases in whicli the direction 

 is different, this is always the result of disturbance. Division at 

 right angles appears to be a common property of the protoplasm of 

 cells in a condition to divide ; and this would seem to be a fact of 

 fundamental importance, although we are altogether in ignorance as 

 to its cause. Whenever an apparent departure is witnessed from this 

 law, it must be the result of forces at work during the division, which 

 deflect the wall from its normal direction. The essential factor in all 

 growth is the increase in volume of the organ on the one hand, and 

 its change in form on the other hand. 



With respect to the formation of cells, the author refers to a view 

 which he has already previously expressed, that many organs which 

 have ordinarily been described as unicellular, are in reality not cel- 

 lular at all. This is especially the case with the Coeloblastas. The 

 ends of the shoots of Gaulerpa, Mucor, &c., play the same part in these 

 plants as the cellular growing point in the higher plants ; and the 

 same is the case with the ends of the shoots of Codium and of the 

 fruticose lichens. The Sphacelariaceae present a beautiful passage 

 between the truly cellular and the non-cellular plants. In this group 

 the whole of the growing part of the plant is non-cellular, and the 

 apical cell corresponds to the earlier growing end of the shoot in 

 higher jdants. The formation, growth, disappearance, and new for- 

 mation of growing points are a consequence of distribution of growth ; 

 the growing point is, however, not the only, although a very common 

 manifestation of this distribution. 



Various Forms of the Cell-nucleus.* — At the conclusion of his 

 paper on " Cell-formation and Cell-division," Professor Strasburger 

 thus sums up the main results arrived at. 



The processes of division are identical in animal and vegetable 

 cells ; as also is the behaviour of the nucleus, with unimportant 

 deviations. The greatest variation which has at present been observed 

 in the division of the nucleus is that between the " nucleus-spindle " 

 with differentiated disk, and the " nucleus-barrel " without any differ- 

 entiated disk. The " nucleus spindle," exclusive of the disk, is com- 

 posed of slender threads usually converging towards the poles ; the 

 " nucleus-barrel " of stronger threads of one kind only, and only slightly 

 approximating towards the poles. The various special forms are 

 classified as under, viz. : — 



I. "Nucleus-spindle"; with differentiation into "threads" and 

 " disk." 

 1. The threads converging strongly towards the poles. 

 a. The poles clearly marked. 



a. The elements of the " plate " uniformly distributed in 

 the equatorial plane of the " spindle." Many animal 

 ova. 

 p. The elements of the " plate " more or less regularly 

 distributed in the equator round the " spindle." En- 

 dothelium of the frog. 



* ' Bot. Zeit.,' xxxvii. (1879) p. 2«1, 



