480 BOTANY 



(b) Sympetalae 

 (a) Pcntacyclicae. 



1. Ericinae : Fain. Ericaceae. Pirolaceae. 

 '2. Diospyrinae : Fam. Sapotaceae. Ebenaceae. Styracaceae. 

 :5. Primulinae : Faiu. Primulaceae. Plumbaginaceae. 



() I'etmcyclicae. 



4. GContortae : Fam. Oleaceac. Loganiaceae. Gentianaceae. Apocynaceae. 



Asclepiadaceae. 



5. Tubifiorae : Fam. Convolvulaceae. Polemoniaceae. Hydrophyllaceae. Bor- 



raginaceae. Verbenaceae. Labiatae. 



6. Personatae : Fam. Solaiiai-cai-. Scrophulariaceae. Orobanchaceae. I'.ig- 



noniaceae. Gesneriaceae. Lentibulariaceae. Acanthaceae. Plantaginaceae. 



7. Hubiinae : Fam. Rubiaceae^ ^fcaprifoliaceae. ValerianaceaeH 

 S.OCampanulinac : Fam. Campanulaceae. Lobeliaceae.CT- Cucurbitaceae.^ 

 9. Aggregatae : Fam. Dipsacaceae. Compositae. 



Class I. Gymnospermae ( 4 ) 



Survey of the Development of the Sexual Generation 



The flowers of the Gymnosperms are all unisexual. The macro- 

 sporophylls form the female, the microsporophylls the male flowers. 

 The two sexes are found either on the same individual (MONOECIOUS) 

 or each plant bears either male or female flowers (DICECIOUS). Leaves 

 forming an envelope around the group of sporophylls are found in 

 only a few flowers of the Gymnospermae. 



The MALE FLOWERS are shoots of limited length, the axis of which bears the 

 closely crowded and usually spirally arranged sporophylls. The scales which 

 invested the flower in the bud often persist at the base of the axis. The micro- 

 sporangia are borne on the lower surface of the sporophylls, two or more In- ing 

 present on each. Their opening is determined as in the sporangia of the Pteri- 

 dophyta by the peculiar construction of the outer layer of cells of the wall 

 (exothecium). The pollen - grains are spherical, and are frequently provided 

 with two sacs filled with air which increase their buoyancy and assist in 

 their distribution by the wind (Fig. 440 D). 



A prothallium consisting of a few cells is formed on the germination of the 

 microspore. This lies within the large cell, which will later give rise to the pollen- 

 tube, closely applied to the cell wall. The prothallium is composed of from 

 1 to 3 cells. The first-formed cells (Fig. 441 A-C, v) correspond to the vegetative 

 cells of the prothallium. The spermatogenous cell (sp) which is cut oft' after these 

 divides later into the mother-cell of the antheridium and a sterile sister-cell (s) 

 adjoining the vegetative cells (Fig. 441 B, D). It is by the breaking down of this 

 latter cell that the antheridial mother-cell becomes free to pass into the pollen- 

 tube. On this taking place, or while the latter cell is still in its original position, 

 it divides into two daughter-cells (y) ; these are the generative cells or the male 

 sexual cells (Fig. 441 E). According to JUKL, Cupressus possesses a larger number of 



