6 GROWTH 



the apical cell, which undergo pronounced subsequent growth. Similarly, 

 in many mushrooms and other large fungi : the products of apical division 

 elongate considerably before ceasing to grow. 



In flowering plants, the embryonic cells form the leaf-primordia, 

 and hence determine the number and position of the appendicular organs, 

 which attain their adult shape by subsequent growth. The first stage in 

 the development of an organ was hence termed by Sachs 2 the morphological 

 period, and the second, the physiological or biological period. It must 

 however be remembered that the progress of development is continuous, 

 so that there is no sharp line of demarcation between the two periods. 



Nor can any sharp line of division be drawn between somatic and 

 embryonic cells, for independently of the fact that under special circum- 

 stances vegetative apices may remain permanently dormant, numerous 

 instances are known of somatic cells returning to an embryonic condition 

 as the result of injury or of other influences. Moreover, such plants as 

 Vaucheria, Mucor, &c., occupy an intermediate position between Soma- 

 tophytes and Asomatophytes, while certain somatophytic fungi when 

 submerged in a culture fluid develop an asomatophytic yeast-form. 



It can easily be understood that the character of the cell is not always 

 indicated by its microscopical appearance. The meristematic cells of flower- 

 ing plants are however usually highly protoplasmic and possess relatively 

 large nuclei. In the cells of Spirogyra however the nucleus is small, and 

 the protoplasm mainly restricted to a peripheral film, but nevertheless 

 the protoplasts remain capable of division and of reproducing new in- 

 dividuals after fusion or rejuvenescence. It is therefore uncertain whether 

 the occurrence of solid protoplasts in primary meristems is mainly for the 

 purpose of allowing rapid subsequent growth in bulk without the mass of 

 protoplasm increasing, or whether this condensation of the protoplast has 

 quite a different importance. 



Every cell and part of a cell, every organ and the entire plant as 

 well, pass more or less rapidly through a specific progress of development 

 whose character is primarily determined by internal causes. This ' grand 

 period of growth 3 ' has definite limits and attains a maximum at a particular 

 phase of development, besides frequently exhibiting secondary maxima. 



1 De Bary, Morphol. u. Biologic d. Pilze, 1884, p. 53 ; A. Mbller, Schimper's hot. Mitthlgn. a. d. 

 Tropen, 1895, Heft 7, p. 119. 



2 For further details see Sachs, Flora, 1893, p. 217; similar views were expressed by Harting, 

 Linnaea, 1847, Bd. XIX, p. 474; cf. also Wiesner, Sitzungsb. d. Wiener Akad., 1883, Bd. LVIII, 

 Abth. i, p. 464. 



s Correctly interpieted by Harting, Linnaea, 1847, Bd. xix, pp. 447, 557 ; Waarnemingen over 

 d. groei van den plantenstengel, 1867 ; cf. also Sachs, Jahrb. f. wiss. Bot., 1860, Bd. n, p. 344 ; 

 Albeit, d. Wiirzburger Instituts, 1874, Bd. I, p. 190 ; and Wiesner, Sitzungsb. d. Wien. Akad., 1883, 

 Bd. LXXXVIII, Abth. i, p. 464. The term 'grand period of growth' was first used by Sachs, 

 Lehrb., 1873, 3. Aufl., p. 731. 



