PHANEROGAMIA 431 



club-shaped mass of tissue termed the nucellus (n). Enveloping the 

 nucellus are one or two sheathing coats, the INTEGUMENTS («), which 

 spring from its basal portion, the so-called CHALAZA (ch). The integu- 

 ments are prolonged beyond the nucellus as a short neck traversed by 

 a canal known as the MlCROPYLE (m). 



Sometimes the axis of the ovules forms a continuous line with the 

 funiculus, the nucellus is then straight (Fig. 361, A), and is said to be 

 ATROPOUS (orthotropous). If the funiculus curves sharply, immediately 

 below the ovule, so that both lie side by side, the ovule is inverted or 

 ANATROPOUS (£). In this, the most frequent case, the funiculus is in 

 part adherent to the outer integument, and forms a suture or raphe 

 on the seed along the line of contact (r). Less frequently the ovule 

 is CAMPYLOTROPOUS (G), and is itself so curved that the chalaza and 

 microphyle do not lie in the same straight line. 



As a rule, only one macrospore, the so-called embryo -SAC, is 

 formed in each nucellus. Unlike the macrospore of the Pterido- 



PHYTES, THE EMBRYO-SAC ALWAYS REMAINS ENCLOSED IN THE MACRO- 

 SPORANGIUM, AND IS ORGANICALLY UNITED WITH IT. In a few cases 



several embryo-sacs are produced in the same nucellus. 



The Sexual Generation — Fertilisation and its Results. — The 

 germinating pollen-grain usually undergoes but one division, from which 

 results the formation of two cells of unequal size. The small cell cor- 

 responds to the antheridium of the Pteridophytes, and eventually gives 

 rise to two generative cells homologous to the spermatozoa, and serving 

 the same purpose. They are devoid of cilia and non-motile. 

 The larger cell represents the whole vegetative portion of the pro- 

 thallium and undergoes no further division. 



The pollen-sacs by this time have attained maturity, and dehiscing 

 by fissures, less frequently by pores, liberate the pollen, which are then 

 dispersed by wind, or carried away by water, or distributed by means 

 of insects. Although a greater part of the pollen is lost, some of the 

 grains are in this way carried to the special portion of the gyncecium 

 adapted for their reception (p. 281). In the Gymnosperms the micro- 

 pyle is the receptive portion ; in the Angiosperms it is the stigma or 

 certain areas of the carpels which are specially adapted, by the excre- 

 tion of a viscid fluid, for the reception of the pollen. In either case, by 

 the protrusion of the intine of the vegetative cell through the germ- 

 pores, tubular outgrowths, the pollen-tubes, are formed which, often 

 after traversing a considerable distance, conduct the two generative cells 

 to the egg-cell. The Phanerogams have accordingly been termed by 

 Engler, Siphonogams (Embryophyta siphonogarna). Pollen-grains will 

 also develop pollen-tubes in a sugary solution or fruit juice. The 

 direction taken by the growing tubes is probably determined, like 

 the movement of the spermatozoa, by chemotactic stimuli. 



A female prothallium with one or more egg-cells is produced 

 in the embryo -sac. The process is not the same in Angiosperms 



