VIII] OF SPORES AND POLLEN 631 



fail to assume, even temporarily, the tetrahedral form: cases, in a 

 general way, where the four cells escape from the confinement of 

 their envelope, and fall into a looser, less close-packed arrangement*. 

 The figures given by Goebel of the development of the pollen* of 

 Neottia (3, a-e\ all the figures referring to grains taken from a 

 single anther) illustrate this to perfection, and it will be seen that, 



Fig. 278. Various pollen-grains and spores (after Berthold, Campbell, Goebe 

 and others). (1) Epilobium; (2) Passiflora; (3) Neottia; (4) Periploca 

 graeca; (5) Apocynum; (6) Erica; (7) spore of Osmuyida; (8) tetraspore of 

 CnUithavinion. 



Fig. 271). I'ollon of bulrush (Tifpha). After Wodehouse. 



when the four cells lie in a plane, they conform exactly to our 

 typical diagram of the first four .cells in a segmenting ovum; 

 physically, as well as biologically, the tetrads a-d and the tetrad e 

 are "allelomorphs" of one another. Again in the bulrush (Fig. 279), 



* Cf. C. Nageli, Znr Entwickhingsgeschichte des Pollens bei den Phanerogamen, 

 36 pp., Zurich, 1842; Hugo Fischer, Vergleichende Morphologie der Pollenkorner, 

 Berlin, 1890; see also, for many and varied illustrations, R. P. Wodehouse's 

 beautiful book on Pollen, 574 pp.. New York, 193o, and earlier papers. 



